                            PUBLISHED

UNITED STATES COURT OF APPEALS
                FOR THE FOURTH CIRCUIT


UNITED STATES OF AMERICA,              
                 Plaintiff-Appellee,
                 v.
RONALD A. MCIVER,
             Defendant-Appellant,                 No. 05-4884
                and
ALL OUT BAIL BONDING; GIGGIES
BONDING COMPANY,
               Parties in Interest.
                                       
           Appeal from the United States District Court
          for the District of South Carolina, at Anderson.
                  Henry F. Floyd, District Judge.
                             (CR-04-745)

                      Argued: September 21, 2006

                      Decided: December 5, 2006

     Before WILKINSON and DUNCAN, Circuit Judges, and
       Richard L. VOORHEES, United States District Judge
 for the Western District of North Carolina, sitting by designation.



Affirmed by published opinion. Judge Duncan wrote the opinion, in
which Judge Wilkinson and Judge Voorhees concurred.


                             COUNSEL

ARGUED: John Philip Flannery, II, CAMPBELL, MILLER & ZIM-
MERMAN, P.C., Leesburg, Virginia, for Appellant. William Corley
2                      UNITED STATES v. MCIVER
Lucius, Assistant United States Attorney, OFFICE OF THE UNITED
STATES ATTORNEY, Greenville, South Carolina, for Appellee. ON
BRIEF: Eli D. Stutsman, Portland, Oregon; C. Rauch Wise, Green-
wood, South Carolina, for Appellant. Jonathan S. Gasser, United
States Attorney, Columbia, South Carolina, for Appellee.


                              OPINION

DUNCAN, Circuit Judge:

   The field of pain management has generated controversy because
of its reliance on opiate-based pain medications (opioids), which are
also a target of the government’s war on drugs. See Diane E. Hoff-
mann & Anita J. Tarzian, Achieving the Right Balance in Oversight
of Physician Opioid Prescribing for Pain: The Role of State Medical
Boards, 31 J. L. Med. & Ethics 21, 22-23 (2003). The government has
recently become more aggressive in prosecuting doctors who unlaw-
fully distribute opioids and other prescription drugs under the guise
of legitimate medical practice. See United States v. Hurwitz, 459 F.3d
463 (4th Cir. 2006); United States v. Feingold, 454 F.3d 1001 (9th
Cir. 2006); United States v. Williams, 445 F.3d 1302 (11th Cir. 2006);
United States v. Alerre, 430 F.3d 681 (4th Cir. 2005). The charges
against Dr. Ronald A. McIver ("Appellant") arose from his prescrip-
tion of pain medications to patients at a pain clinic. He appeals his
conviction for various counts of unlawful distribution of a controlled
substance, unlawful distribution of a controlled substance resulting in
death, and conspiracy to unlawfully distribute a controlled substance.
For the reasons that follow, we affirm.

                                   I.

    Appellant is a doctor of osteopathic medicine1 who was licensed to
    1
   "A doctor of osteopathic medicine (D.O.) is a physician licensed to
perform surgery and prescribe medication." MedlinePlus Medical Ency-
clopedia: Doctor of Osteopathy (D.O.), http://www.nlm.nih.gov/
medlineplus/ency/article/002020.htm. Osteopaths differ from doctors of
medicine ("M.D.") in that they receive specialized training in "hands-on
manual medicine and the body’s musculoskeletal system," and are "dedi-
cated to treating and healing the entire patient as a whole, rather than
focusing on one system or body part." Id. In practice, however, the roles
of D.O.’s and M.D.’s are often identical.
                        UNITED STATES v. MCIVER                           3
prescribe controlled substances under the Controlled Substances Act,
21 U.S.C. § 801 et seq. He operated a medical clinic in Greenwood,
South Carolina that specialized in treating chronic pain. The United
States Drug Enforcement Administration ("DEA") began investigat-
ing Appellant in 2002 after receiving information about his prescrib-
ing practices from the Columbia, South Carolina police department.
J.A. 682-83.2 During its investigation, the DEA discovered that
Appellant had prescribed massive quantities of oxycodone,3 Dilaudid,4
OxyContin,5 methadone,6 and morphine7 to his patients. J.A. 687-88.
The investigation also uncovered a disturbing pattern among Appel-
lant’s patients. These patients included admitted drug addicts who
traveled significant distances to see him, appeared without referrals,
paid in cash, and sought specific drugs which were prescribed for
them based on little or no physical examination.

   The government indicted Appellant on fifteen counts related to his
treatment of ten patients, nine of whom testified for the government
at trial. The remaining patient, Larry Shealy, was deceased; his death
formed the basis of two counts of the indictment.

  2
     Our citations to "J.A. ___" refer to the contents of the Joint Appendix
filed by the parties in this appeal.
   3
     Oxycodone is a potent and addictive opioid that is classified as a
Schedule II drug under the Controlled Substances Act. See 21 U.S.C.
§ 812 (2000); 21 C.F.R. § 1308.12(b)(1) (2004). It is marketed in instant-
release form under trade names such as Roxicodone, Roxicet, OxyIR,
and OxyFAST, and in a controlled- release form as OxyContin.
   4
     Dilaudid is the trade name for a medication that contains hydromor-
phone, a potent and addictive opioid that is classified as a Schedule II
narcotic. § 1308.12(b)(1).
   5
     OxyContin is the trade name of a controlled-release form of oxyco-
done that can be crushed to circumvent the time-release mechanism and
then taken either nasally or intravenously.
   6
     Methadone is a potent and addictive synthetic opioid that is used to
treat pain and addiction to other opioids. It is classified as a Schedule II
narcotic. § 1308.12(b)(1).
   7
     Morphine is one of the most powerful and addictive opioids. It is clas-
sified as a Schedule II narcotic. § 1308.12(b)(1).
4                      UNITED STATES v. MCIVER
   After trial, the jury convicted Appellant of one count of conspiracy
to distribute controlled substances unlawfully in violation of 21
U.S.C. § 846 (2000) (Count 1), six counts of unlawful distribution of
a controlled substance in violation of 21 U.S.C. § 841(a)(1) (2000)
(Counts 3-5, 13-15), and two counts of unlawful distribution of a con-
trolled substance resulting in the death of Larry Shealy in violation of
§ 841(a)(1) & (b)(1)(C) (Counts 11, 12).8 The district court sentenced
Appellant to 240 months on Counts 1, 3, 4, 5, 13, 14, and 15, and 360
months on Counts 11 and 12, to run concurrently. Appellant timely
appealed.

   We turn now to a consideration of the facts relevant to this appeal,
beginning with those involving the six patients whose experiences
underlie Appellant’s convictions. In the context of Appellant’s chal-
lenges to the sufficiency of the evidence, we recite those facts in the
light most favorable to the government. United States v. Rahman, 83
F.3d 89, 93 (4th Cir. 1996). We then discuss the testimony of the gov-
ernment’s expert witness, Dr. Steven Storick, and the district court’s
jury instruction on the § 841(a)(1) charges.

    A. Larry Shealy

   Larry Shealy sought treatment from Appellant for back and knee
pain. J.A. 416. Appellant treated Shealy almost exclusively with large
quantities of various simultaneous combinations of morphine, Oxy-
contin, oxycodone, and methadone. J.A. 526. Shealy’s son, who
accompanied his father to many of his appointments, only observed
his father receive non-drug therapy once. J.A. 416-17.

   Shealy’s son testified that after Shealy started seeing Appellant, his
father’s demeanor changed dramatically. J.A. 417-19. In addition to
losing his appetite and weight, Shealy became somnolent and irrita-
ble. J.A. 418. On one occasion, Shealy backed his truck into a tree,
apparently without realizing he had done so. J.A. 417-18. These
changes so worried Shealy’s son that he counseled his father to stop
seeing Appellant. J.A. 419. Shealy, however, continued seeing Appel-
lant until he died from an oxycodone overdose. J.A. 419-20, 427-30,
    8
   McIver was acquitted of all charges relating to four patients, identi-
fied as "A," "E," "F," and "G" in the indictment. J.A. 15-20.
                      UNITED STATES v. MCIVER                        5
456. The level of drugs in Shealy’s system when he died was consis-
tent with the amounts Appellant prescribed. J.A. 427-30.

  A representative of the company that provided Shealy health insur-
ance testified that the amount and cost of the drugs prescribed to
Shealy, along with the frequency of dosage, "was as high as [he had]
ever seen." J.A. 134-35. The representative became so concerned
about Shealy’s prescriptions that he contacted the DEA. J.A. 134.

  B. Barbee Brown

   Barbee Brown sought treatment from Appellant primarily for reflex
sympathetic dystrophy, a chronic neurological condition that causes
severe pain. J.A. 518-19. Appellant knew from the outset that Brown
had a history of prescription drug and cocaine abuse. J.A. 207-08,
519. He nevertheless prescribed OxyContin, oxycodone, and, later,
methadone in various simultaneous combinations for her. J.A. 518-23.
Appellant also allowed Brown to manage her own dosing without
specifying a maximum amount. J.A. 208. Brown’s father wrote to
Appellant to express concern about his daughter’s treatment, stating
that, since coming to see Appellant, Brown had been in a "drug state,"
"unstable in her speech and ha[d] threatened to kill" her father. J.A.
233, 520. Appellant continued prescribing opioids to Brown, how-
ever, maintaining that, if anything, her dose was too low. J.A. 521.

   Appellant stopped treating Brown abruptly after less than two
months when her insurance stopped covering his care. J.A. 211. He
took no steps to wean her from the opioids, however, and she was
hospitalized for four days with severe drug withdrawal symptoms.
J.A. 211-12.

  C. Leslie Smith

   Leslie Smith sought treatment from Appellant specifically to obtain
prescription painkillers. J.A. 176. Smith traveled sixty miles each way
to see Appellant after learning that he had readily prescribed drugs to
one of Smith’s friends. J.A. 175-76. Smith testified that he lied to
Appellant about pain in his wrist, but that Appellant prescribed high
doses of OxyContin and Dilaudid, the drugs that Smith requested,
6                      UNITED STATES v. MCIVER
without ordering x-rays. J.A. 178, 180-183. At trial, Smith admitted
that he was a drug addict and injected these drugs to satisfy his habit.
J.A. 176. Evidence indicates that Appellant was aware of Smith’s
drug use; Appellant discovered a syringe in Smith’s possession during
a visit, but on being told that Smith used it for fishing, continued to
prescribe Smith’s drugs. J.A. 185.

   Appellant eventually became sufficiently suspicious that Smith was
either using or selling his medications to write to the South Carolina
Department of Health and Environmental Control to express those
concerns. J.A. 180-81, 684. Appellant, however, continued prescrib-
ing drugs to Smith after writing the letter. J.A. 181-82.

    D. Seth Boyer

   Like Smith, Seth Boyer learned of Appellant from friends and
began traveling more than an hour to see him specifically to obtain
prescription drugs. J.A. 248, 250-51. Boyer came to his first appoint-
ment with Appellant with track marks on his arms from intravenous
drug use. J.A. 250-51, 253. Boyer complained of pain in his foot, but,
as with Smith, Appellant did not x-ray it before prescribing OxyCon-
tin, OxyFast, and Dilaudid. J.A. 249-50, 253. Boyer both used and
sold these drugs. J.A. 253. On one occasion, Boyer lied to Appellant
about spilling a bottle of liquid oxycodone, and Appellant refilled the
prescription immediately. J.A. 255.

    E. Kyle Barnes

   Kyle Barnes started seeing Appellant for treatment of fibromyalgia,
a chronic condition characterized by widespread pain and stiffness,
after her former provider was closed by the government because of
its prescribing practices. J.A. 347. When Appellant first began treat-
ing her, Barnes was addicted to oxycodone. J.A. 346. Even though
Barnes was poor and receiving Medicaid, she traveled nearly three
hours to see Appellant, paid for his services in cash and filled pre-
scriptions for thousands of dollars worth of medications. J.A. 350,
353, 359, 530.

  Appellant prescribed Barnes massive doses of methadone, Oxy-
Contin, oxycodone and morphine in various simultaneous combina-
                       UNITED STATES v. MCIVER                        7
tions. J.A. 354, 356, 529. In one year, Appellant prescribed Barnes
20,562 individual doses of various medications. J.A. 687. Appellant
continued to prescribe methadone even after Barnes told him that she
could not take it because of side effects. J.A. 354, 356. Barnes sold
both the methadone and morphine. J.A. 356, 359.

   Evidence supports an inference that Appellant knew Barnes was
not taking her medicine as prescribed. At one point after Appellant
had prescribed Barnes high doses of opioids for a number of months,
she reported running out of her medications. J.A. 530-31. She did not,
however, report any of the withdrawal symptoms commonly associ-
ated with a sudden cessation of such high doses. J.A. 530-31.

  F. Angela Knight

   Angela Knight sought treatment from Appellant for chronic back
pain after her previous pain clinic was shut down for its prescribing
practices. J.A. 388-89. Even though she lived closer to other pain
clinics, Knight traveled nearly two-and-one-half hours to see Appel-
lant. J.A. 392, 542. He treated Knight with high doses of OxyContin,
along with methadone and oxycodone. J.A. 538-40.

   As with other of Appellant’s patients, evidence suggested that
Knight was not taking her medicine as prescribed. For example, at her
former pain clinic, Knight twice tested negative for opioids despite
being prescribed OxyContin at the time. J.A. 537-38. Even though her
medical records revealed this fact, on her first visit to him, Appellant
doubled the dosage of her previous OxyContin prescription. J.A. 390.
Thereafter, Appellant continued to prescribe high and escalating
doses of opioids for Knight after his office conducted two similar
drug tests that detected no opioids in her system. J.A. 538, 542.

   On other occasions, Knight tested positive for opioids, indicating
that she was, in fact, taking her medications. J.A. 539-40. Knight
eventually became addicted to the medications that Appellant pre-
scribed and suffered significant withdrawal when she stopped taking
them. J.A. 397.

  G. Dr. Steven Storick’s Testimony

  At trial, the government offered testimony from Dr. Steven Storick
("Dr. Storick"), an anesthesiologist qualified as an expert in pain man-
8                        UNITED STATES v. MCIVER
agement. Based on his review of certain patient records, Dr. Storick
concluded that the treatment of several of Appellant’s patients fell
outside the parameters of legitimate medical practice.

   With respect to Shealy, for example, Dr. Storick testified that there
was "no legitimate reason to be prescribing" combinations of opioids
in such high doses based on the patient’s medical conditions. J.A.
527. Similarly, given Brown’s history of drug abuse, Storick testified
that Appellant’s treatment went "outside the course of legitimate med-
ical practice," and was "like pouring gasoline onto a fire." J.A. 523.

   As to Barnes, Dr. Storick stated that it was uncommon to treat
fibromyalgia with the amount and type of medication Appellant pre-
scribed. J.A. 533. Indeed, he testified that Appellant’s treatment of
her "was one of the worst cases [he had] seen" and that "it was way
outside the course of legitimate medical treatment." J.A. 534. In
response to questions about Ms. Knight, Dr. Storick testified that it
was outside the legitimate practice of medicine for Appellant to pre-
scribe high doses of opioids given her history of negative drug
screens. J.A. 542-43.

   Dr. Storick was subjected to rigorous cross-examination regarding
varying theories of pain management, and acknowledged differences
in points of view as to appropriate levels of pain medication. J.A.
576-80. He was also challenged as to, and defended his opinions
regarding, Appellant’s treatment of specific patients.

    H. Jury Instructions for § 841(a)(1) Charges

   Under § 841(a)(1), the government must prove (1) that Appellant
knowingly or intentionally distributed a controlled substance; (2) with
knowledge that it was controlled under the law; and (3) that he did
so "outside the usual course of professional practice." United States
v. Moore, 423 U.S. 122, 124 (1975); see also United States v. Tran
Trong Cuong, 18 F.3d 1132, 1137 (4th Cir. 1994) (setting out ele-
ments of § 841(a)(1) charge). With respect to the third element—the
only one challenged by Appellant on appeal—the district court
instructed the jury extensively prior to its deliberations.9
    9
     The court instructed the jury in relevant part as follows:
        There are no specific guidelines concerning what is required
                       UNITED STATES v. MCIVER                            9
                                   II.

   On appeal, Appellant argues that: (1) the district court’s instruc-
tions on the § 841(a)(1) charges improperly lowered the government’s

   to support a conclusion that a defendant physician acted outside
   the usual course of professional practice and for other than a
   legitimate medical purpose. In making a medical judgment con-
   cerning the right treatment for an individual patient, physicians
   have discretion to choose among a wide range of options. There-
   fore, in determining whether a defendant acted without a legiti-
   mate medical purpose, you should examine all of a defendant’s
   actions and the circumstances surrounding the same.
      If a doctor dispenses a drug in good faith, in medically treating
   a patient, then the doctor has dispensed that drug for a legitimate
   medical purpose in the usual course of medical practice. That is,
   he has dispensed the drug lawfully.
      Good faith in this context means good intentions, and the hon-
   est exercise of professional judgment as to the patient’s needs.
   It means that the defendant acted in accordance with what he
   reasonably believed to be proper medical practice. If you find
   that a defendant acted in good faith in dispensing the drugs
   charged in this indictment, then you must find that defendant not
   guilty.
      For you to find that the government has proven this essential
   element, you must determine that the government has proven
   beyond a reasonable doubt that the defendant was acting outside
   the bounds of professional medical practice, as his authority to
   prescribe controlled substances was being used not for treatment
   of a patient, but for the purpose of assisting another in the main-
   tenance of a drug habit or dispensing controlled substances for
   other than a legitimate medical purpose, in other words, the per-
   sonal profit of the physician.
      Put another way, the government must prove as to each count
   beyond a reasonable doubt that the defendant dispensed the spe-
   cific controlled substance other than for a legitimate medical
   purpose and not with the bounds of professional medical prac-
   tice.
     A physician’s own methods do not themselves establish what
   constitutes medical practice. In determining whether the defen-
10                       UNITED STATES v. MCIVER
burden of proof; (2) Dr. Storick’s expert testimony constituted inad-
missible legal opinions; (3) the district court erred in excluding evi-
dence from Appellant’s expert witness, Dr. Thomas Duc; and (4)

     dant’s conduct was within the bounds of professional practice,
     you should, subject to the instructions I give you concerning the
     credibility of experts and other witnesses, consider the testimony
     you have heard relating to what has been characterized during
     the trial as the norms of professional practice.
        You should also consider the extent to which, if at all, any vio-
     lation of professional norms you find to have been committed by
     the defendant interfered with his treatment of his patients and
     contributed to an over prescription and/or excessive dispensation
     of controlled substances. You should consider the defendant’s
     actions as a whole and the circumstances surrounding them. A
     physician’s conduct may constitute a violation of applicable pro-
     fessional regulations as well as applicable criminal statutes.
     However, a violation of a professional regulation does not in and
     of itself establish a violation of the criminal law. As I just indi-
     cated, in determining whether or not the defendant is guilty of
     the crimes with which he is charged, you should consider the
     totality of his actions and the circumstances surrounding them
     and the extent and severity of any violations of professional
     norms you find he committed. . . .
        There has been some mention in this case from time to time
     of the standard of care. During the trial the words medical mal-
     practice may have been used. Those words relate to civil actions.
     When you go to see a doctor, as a patient, that doctor must treat
     you in a way so as to meet the standard of care that physicians
     of similar training would have given you under the same or simi-
     lar circumstances. And if they fall below that line or what a rea-
     sonable physician would have done, then they have not exercised
     that standard of care, which makes them negligent and which
     subjects themselves to suits for malpractice.
        That is not what we’re talking about. We’re not talking about
     this physician acting better or worse than other physicians.
     We’re talking about whether or not this physician prescribed a
     controlled substance outside the bounds of his professional medi-
     cal practice.
J.A. 1291-96.
                        UNITED STATES v. MCIVER                         11
there was insufficient evidence to support each of his convictions. We
consider each argument in turn.

                                    A.

                                    1.

   Appellant first argues that by referring to "norms of professional
practice" in the jury instructions, the district court improperly allowed
the jury to convict on a civil, rather than a criminal, standard of proof.
We review the accuracy and adequacy of jury instructions de novo,
United States v. Scott, 424 F.3d 431, 434 (4th Cir. 2005), and will not
reverse a conviction so long as "the instructions, taken as a whole,
adequately state the controlling law," United States v. Wills, 346 F.3d
476, 492 (4th Cir. 2003) (emphasis added). Because we find that the
district court’s instructions as a whole adequately articulated a crimi-
nal standard of proof, we find no error.

   The potential for juries to confuse the civil standard of care applied
in medical malpractice cases and the criminal standard of proof
applied in § 841(a)(1) prosecutions requires courts to exercise care in
setting out the governing standard in the latter circumstance.10 We
have previously considered the proper relationship between the stan-
dards in two decisions that are relevant to our analysis here, even
though neither involved a direct challenge to the propriety of
§ 841(a)(1) jury instructions.

   In Tran Trong Cuong, we addressed a sufficiency of the evidence
challenge by Tran, a physician also indicted under § 841(a)(1). Tran’s
argument in part was that the district court erroneously applied a civil
negligence, rather than a criminal, standard of proof during trial. 18
  10
    In Alerre we pointed out that, "[i]n contrast to the criminal standard,
a medical malpractice plaintiff in South Carolina must show in a civil
case (1) ‘the generally recognized practices and procedures that would be
exercised by competent practitioners in a defendant doctor’s field of
medicine under the same or similar circumstances,’ and (2) ‘that the
defendant doctor departed from the recognized and generally accepted
standards, practices, and procedures.’" 430 F.3d at 690 (citing Gooding
v. St. Francis Xavier Hosp., 487 S.E.2d 596, 599 (S.C. 1997)).
12                    UNITED STATES v. MCIVER
F.3d at 1137. While acknowledging that the district court had, during
trial, confused the two standards, we nevertheless concluded that the
court’s articulation of the criminal standard was correct when it
instructed the jury at the close of the case. Id. at 1137-38. The trial
court made it clear in its jury charge that the government must "prove
beyond a reasonable doubt . . . that the defendant prescribed the drug
other than for [a] legitimate medical purpose and not in the usual
course of medical practice." Id. at 1137. It then recognized the broad
discretion afforded doctors, instructed the jury to consider all of the
defendant’s actions, and provided specific examples of behavior that
tended to denote illegitimacy, such as prescribing drugs without per-
forming physical examinations, or asking patients about the amount
or type of drugs they want. Id. at 1137-38. We held that these instruc-
tions adequately articulated the government’s criminal burden of
proof, and did not endorse the use of a negligence standard. Id.
Indeed, we concluded that the jury instructions not only captured the
criminal standard, but arguably imposed a higher burden on the gov-
ernment than set forth in Moore by additionally requiring proof that
Tran had written prescriptions "without a legitimate medical pur-
pose." Id.

   In Alerre, in response to an argument that the entire trial was
infected with an erroneous standard of proof, we approved instruc-
tions that largely mirrored those in Tran Trong Cuong but more fully
developed "the distinction between the civil standard and the criminal
standard." 430 F.3d at 691 n.9. The district court in Alerre distin-
guished civil standard-of-care evidence, explained the burden of proof
necessary for a criminal conviction, and cautioned the jury that "the
critical issue . . . was not whether the defendants had acted negli-
gently, but whether or not [they] prescribed a controlled substance
outside the bounds of their professional medical practice." Id. (quota-
tions omitted).

   Significantly, we recognized in Alerre that merely because
standard-of-care evidence might show that a physician contravened
the civil standard, it need not be categorically excluded from a crimi-
nal proceeding. Id. at 691. To the contrary, "evidence that a physician
consistently failed to follow generally recognized procedures tends to
show that in prescribing drugs he was not acting as a healer but as a
seller of wares." Id. Similarly, we recognized that evidence that a
                       UNITED STATES v. MCIVER                         13
physician "deviated drastically from accepted medical standards" is
probative of criminal liability. Id.

   With that guidance, we consider the challenge before us, which
specifically focuses on the district court’s jury instructions. The thrust
of Appellant’s argument is that the district court erred in telling the
jury to consider the extent to which "any violation of professional
norms you find to have been committed by the defendant interfered
with his treatment of his patients and contributed to an over prescrip-
tion and/or excessive dispensation of controlled substances." J.A.
1293. Appellant specifically focuses on the district court’s use of the
phrase "norms of professional practice." However, after reviewing the
jury instructions as a whole, as we must, Wills, 346 F.3d at 492, we
find multiple reasons to conclude that the instructions here properly
set forth the criminal standard required by § 841(a)(1).

   As was the case in Tran Trong Cuong, 18 F.3d at 1137, and Alerre,
430 F.3d at 687, the court below cabined both its overall § 841(a)(1)
instruction, as well as its specific instructions on the third element,
within the requirement of proof "beyond a reasonable doubt." J.A.
1290, 1292. This statement clearly articulated the proper criminal bur-
den for the government and precluded conviction on a lesser civil
standard of proof.

   The court then properly defined the scope of unlawful conduct
under § 841(a)(1) by explaining that the government had to prove that
Appellant used "his authority to prescribe controlled substances . . .
not for treatment of a patient, but for the purpose of assisting another
in the maintenance of a drug habit or" some other illegitimate pur-
poses, such as his own "personal profit." J.A. 1292; see Alerre, 430
F.3d at 690-91. This instruction set the proper threshold for convic-
tion by placing unlawful conduct beyond the bounds of any legitimate
medical practice, including that which would constitute civil negli-
gence. See Tran Trong Cuong, 18 F.3d at 1137; cf. Alerre, 430 F.3d
at 690 (setting forth the standard for medical malpractice in South
Carolina). In other words, the district court ensured that the jury could
only convict Appellant for conduct that was exclusively criminal in
nature.

   Significantly, in order to satisfy this definition of unlawful conduct,
the district court required the prosecution to prove, not only that
14                     UNITED STATES v. MCIVER
Appellant acted "outside the course of professional practice," as
required by Moore, 423 U.S. at 124, but also that he acted "for other
than a legitimate medical purpose," J.A. 1292 (emphasis added). This
additional requirement arguably benefitted Appellant by placing an
even heavier burden on the government than otherwise required to
establish criminal liability. See Alerre, 430 F.3d at 690-91; Tran
Trong Cuong, 18 F.3d at 1138.

   As in Tran Trong Cuong, 18 F.3d at 1138, and Alerre, 430 F.3d
at 691 n.9, the court next stated that so long as Appellant acted in
good faith, he acted lawfully. J.A. 1291-92; see 430 F.3d at 692; 18
F.3d at 1138. The significance of this distinction is manifest: good
faith is a defense to a charge under § 841(a)(1), but not to a claim of
medical malpractice. See Hurwitz, 459 F.3d at 480 ("good faith gener-
ally is relevant in a § 841 case against a registered physician"); Pleas-
ants v. Alliance Corp., 209 W. Va. 39, 49 n.27 (2000) (collecting
cases rejecting use of subjective good faith jury instructions in medi-
cal malpractice actions). The inclusion of a good faith instruction is
therefore a plainspoken method of explaining to the jury a critical dif-
ference between the two standards.

   Finally, the court instructed the jury on the difference between civil
and criminal violations. J.A. 1293. The court indicated that "a viola-
tion of a professional norm does not in and of itself establish a viola-
tion of [a] criminal law," but could support a conviction based on its
"extent and severity." Id. While this instruction allowed the jury to
consider civil violations, it properly explained that such evidence is
not inexorably indicative of unlawfulness. See Alerre, 430 F.3d at
691. The district court then concluded by describing the concept of
medical malpractice and the civil standard of care before categorically
stating that a criminal standard governed resolution of this case.11 J.A.
1293-96 ("[Malpractice or negligence] is not what we’re talking about
  11
    While not directly relevant to the distinction between a civil and
criminal standard of proof, we further note that the court here mirrored
the instructions in both Tran Trong Cuong, 18 F.3d at 1137-38, and
Alerre, 430 F.3d at 691 n.9, by instructing the jury to base its decision
on all of Appellant’s actions and the surrounding circumstances. J.A.
1291. Appellant thus received the benefit of court-sanctioned deference
to his professional judgment.
                        UNITED STATES v. MCIVER                         15
. . . . We’re talking about whether or not this physician prescribed a
controlled substance outside the bounds of his professional medical
practice.").

   These instructions, taken as a whole, set the proper threshold for
conviction, mandating application of a criminal standard of proof and
precluding conviction on a lower civil standard. The fact that the dis-
trict court may have invoked language, taken in isolation, suggestive
of a civil standard, would not alone lower the government’s burden
of proof. Indeed, it would be difficult, if not impossible, to purge an
instruction under § 841(a)(1) of all references to permissible stan-
dards or norms of care, since the third element of § 841(a)(1) requires
a determination of whether the defendant’s conduct is outside the
usual course of professional conduct.

   The jury instructions here went further in defining the proper crimi-
nal standard and distinguishing it from the civil standard than those
which we approved, albeit in different contexts, in both Tran Trong
Cuong and Alerre. We therefore find no error with the district court’s
instructions.

                                    2.

   Appellant further argues that Dr. Storick’s testimony combined
with the instructions on the third element to lower the government’s
burden. At trial, Dr. Storick opined that Appellant acted "outside the
course of legitimate medical practice," "inappropriate[ly]" or "with no
legitimate reason." J.A. 523, 527, 543. Appellant argues that the con-
fluence of this testimony and the court’s instructions regarding the
"norms of professional practice" effectively allowed the jury to con-
vict based on a civil standard of proof. We find this argument unper-
suasive for two reasons.

   First, as we recognized in Alerre and noted above, evidence regard-
ing a departure from a generally recognized standard-of-care is not
inherently impermissible. 430 F.3d at 691. To the contrary, such evi-
dence may support an inference that a physician is acting as a dealer
of drugs rather than a provider of care.12 Id. Indeed, it is the extent and
  12
   We entrust to the district court the task of ensuring that such evi-
dence is sufficiently constrained as to not confuse a jury. See Fed. R.
16                     UNITED STATES v. MCIVER
severity of departures from the professional norms that underpin a
jury’s finding of criminal violations. See id. ("[E]vidence that a physi-
cian consistently failed to follow generally recognized procedures
tends to show that in prescribing drugs he was not acting as a healer
but as a seller of wares.")

   Second, even if we assume that Dr. Storick suggested a lower bur-
den to the jury, the district court’s jury charge negated any such testi-
mony by articulating the proper standard. Again, our decision in Tran
Trong Cuong is instructive. The district court there made statements
at trial that unambiguously indicated that a civil standard of proof
governed the case, commenting, for example, that the governing stan-
dard was (1) "whether a reasonably prudent physician would do it,"
(2) "whether it is within the standard of care of a family practitioner,"
and (3), "like you use in a civil case, whether [care was comparable
to that provided] in the usual course of treating a patient by the aver-
age family practitioner." 18 F.3d at 1137. We concluded, nonetheless,
that the satisfactory definition included in the jury instructions cured
the prior misstatements. Id. at 1138. Such a conclusion is consistent
with our general presumption that "a properly instructed jury [acts] in
a manner consistent with the instructions." Alerre, 430 F.3d at 692;
see Jones v. United States, 527 U.S. 373, 394 (1999) ("[J]urors are
presumed to have followed . . . instructions.").

   As discussed above, the district court here instructed the jury that
the government had to satisfy a criminal standard of proof to convict
Appellant. J.A. 1291-96. We presume that the jury followed these
instructions and ignored any suggestion to the contrary. See Jones,
527 U.S. at 394; Alerre, 430 F.3d at 692. We discern nothing in the
record that rebuts this presumption. Accordingly, we find no error.

                                   B.

   Appellant next asserts error in the admission of Dr. Storick’s expert
testimony that Appellant treated certain patients outside the course of

Evid. 403 (requiring exclusion of confusing evidence); Alerre, 430 F.3d
at 691 n.10 (noting that "undue emphasis on standard-of-care evidence
might, in certain circumstances, confuse a jury."). Based on the record
before us, we find nothing improper with the evidence admitted at trial.
                       UNITED STATES v. MCIVER                         17
legitimate medical practice. Appellant argues that this testimony
embraced inadmissible legal conclusions. We review this argument
for plain error because Appellant did not object to the testimony at
trial. United States v. Ellis, 121 F.3d 908, 918 (4th Cir. 1997). To
reverse on plain error review, we "must ‘(1) identify an error, (2)
which is plain, (3) which affects substantial rights, and (4) which seri-
ously affect[s] the fairness, integrity or public reputation of judicial
proceedings.’" Id. (quoting United States v. Brewer, 1 F.3d 1430,
1434 (4th Cir. 1993)) (alterations in original). Because we conclude
that Dr. Storick’s testimony was admissible, there was no error and
Appellant cannot satisfy this standard.

   Rule 704(a) allows the admission of expert testimony that "em-
braces an ultimate issue to be decided by the trier of fact." Fed. R.
Evid. 704(a). In other words, questions of fact that are committed to
resolution by the jury are the proper subject of opinion testimony. Id.
However, opinion testimony that states a legal standard or draws a
legal conclusion by applying law to the facts is generally inadmissible.13
See United States v. Barile, 286 F.3d 749, 760 (4th Cir. 2002);
Okland Oil Co. v. Conoco, Inc., 144 F.3d 1308, 1328 (10th Cir.
1998). The line between a permissible opinion on an ultimate issue
and an impermissible legal conclusion is not always easy to discern.
Barile, 286 F.3d at 760. We identify improper legal conclusions by
determining whether "the terms used by the witness have a separate,
distinct and specialized meaning in the law different from that present
in the vernacular." Id. For example, courts have held inadmissible tes-
timony that a defendant’s actions constituted "extortion," DiBella v.
Hopkins, 403 F.3d 102, 121 (2d Cir. 2005); that a dog bite constituted
"deadly force," Miller v. Clark County, 340 F.3d 959, 963 n.7 (9th
Cir. 2003); that defendants held a "fiduciary" relationship to plain-
tiffs, Christiansen v. Nat’l Sav. & Trust Co., 683 F.2d 530, 529 (D.C.
  13
     We have previously recognized that in certain circumstances, such as
cases involving specialized industries, "opinion testimony that arguably
states a legal conclusion is helpful to the jury, and thus, admissible."
United States v. Barile, 286 F.3d 749, 760 n.7 (4th Cir. 2002) (quoting
Weinstein’s Federal Evidence § 704.04[2][a] (2d ed. 2001)). Because we
conclude that Dr. Storick’s testimony did not embrace improper legal
conclusions, we need not confront the question of whether his testimony
falls under this exception.
18                       UNITED STATES v. MCIVER
Cir. 1982); and that a product was "unreasonably dangerous," Strong
v. E.I. DuPont de Nemours Co., 667 F.2d 682, 685-86 (8th Cir. 1981).
Dr. Storick’s testimony, however, does not involve terms with similar
legal significance.

   On the issue of whether Appellant acted "outside the bounds of his
professional medical practice and for other than legitimate medical
purposes," Tran Trong Cuong, 18 F.3d at 1137,14 Dr. Storick opined
that Appellant’s treatment of certain patients was either illegitimate
or inappropriate. J.A. 523, 527, 534, 541, 557-58. Although Dr. Stor-
ick used terms similar to that which this court has employed to
express the underlying issue, none is sufficiently specialized to render
his testimony inadmissible. Rather, the language Dr. Storick
employed falls within the limited vernacular that is available to
express whether a doctor acted outside the bounds of his professional
practice.15 We conclude therefore that the district court properly
admitted Dr. Storick’s testimony and that Appellant cannot establish
plain error.

                                     C.

   Appellant argues that the district court erred by excluding testi-
mony from his expert witness, Dr. Thomas Duc. During direct exami-
nation, Appellant’s attorney asked Dr. Duc whether a minority group
of doctors who treat pain aggressively with opioids acted "within the
bounds of medical practice." J.A. 1085. The government raised an
objection to this testimony, which the district court sustained, on the
  14
      This issue is a question of fact that is entrusted to the jury, see Tran
Trong Cuong, 18 F.3d at 1137-38 (approving instructions given to jury
on this issue); United States v. Kaplan, 895 F.2d 618, 623-24 (9th Cir.
1990) (treating issue as question for jury); Oregon v. Ashcroft, 192 F.
Supp. 2d 1077, 1090 n.15 (D. Or. 2002) (recognizing issue as a question
of fact for jury), and, therefore, is the proper subject of expert testimony,
see Fed. R. Evid. 704(a).
   15
      We note as well that experts in Tran Trong Cuong and Alerre testi-
fied similarly, and that the defendant in Tran Trong Cuong relied on the
opinions of two physicians that his prescription practices were "within
the state of the art" or "the medical standard." 430 F.3d at 686; 18 F.3d
at 1135.
                       UNITED STATES v. MCIVER                        19
grounds that it called for a legal conclusion. Id. Even if the district
court’s exclusion of this testimony were improper, any such error was
harmless because of the examination that followed. See United States
v. Pendergraph, 388 F.3d 109, 112 (4th Cir. 2004) (recognizing that
error in exclusion of evidence is harmless if it does not substantially
sway the judgment).

   After the district court sustained the government’s objection,
Appellant’s attorney reworded his inquiry and conducted, without
objection, a thorough examination of Dr. Duc’s opinions on various
approaches to pain management. J.A. 1085-88. This testimony was
substantively identical to that sought from the initial question; it was
merely elicited through an unobjectionable, if somewhat more cum-
bersome, line of questioning. Because of the similarity between the
two lines of inquiry, we conclude that any error in the exclusion of
the initial line of questioning did not sway the jury and, therefore, was
harmless.

                                   D.

   Finally, Appellant argues that there was insufficient evidence to
support each of his convictions. A "jury’s verdict must be upheld on
appeal if there is substantial evidence in the record to support it."
United States v. Wilson, 198 F.3d 467, 470 (4th Cir. 1999). In making
this determination, "we view the evidence in the light most favorable
to the government and inquire whether there is evidence that a ‘rea-
sonable finder of fact could accept as adequate and sufficient to sup-
port a conclusion of a defendant’s guilt beyond a reasonable doubt.’"
Id. (quoting United States v. Burgos, 94 F.3d 849, 862 (4th Cir. 1996)
(en banc)). We now turn to an analysis of each claim.

  1. Count 1, Conspiracy to Unlawfully Distribute a Controlled
     Substance

   Appellant argues that the government did not present sufficient evi-
dence on Count 1 to prove either that he entered into an illicit agree-
ment with his patients to distribute controlled substances unlawfully
or that he did so knowingly. Proof of each was a necessary element
of the conspiracy charge against him. United States v. Cropp, 127
F.3d 354, 361 (4th Cir. 1997); United States v. Clark, 928 F.2d 639,
20                     UNITED STATES v. MCIVER
641-42 (4th Cir. 1991). There is ample evidence, however, to support
each element.

   With respect to the first element, "it is not necessary to prove a for-
mal agreement to establish a conspiracy in violation of federal law;
a tacit or mutual understanding among or between the parties will suf-
fice." United States v. Depew, 932 F.3d 324, 326 (4th Cir. 1991).
There was evidence that many of Appellant’s patients were drug
addicts who sought treatment from him with the express purpose of
obtaining drugs and, further, that he prescribed drugs in quantities
greater than he had reason to believe, or that tests revealed, his
patients were using. See J.A. 134-35, 176, 248, 354, 356, 523, 527,
529, 533-34, 538-40, 543, 687. Viewed in a light most favorable to
the government, this evidence supports a conclusion that McIver tac-
itly agreed with his patients to provide opioid prescriptions without
legitimate medical reasons for doing so.

   The government can satisfy the knowledge requirement by show-
ing either that Appellant actually knew of the conspiracy, Cropp, 127
F.3d at 361, or that he was willfully blind to it by "purposely clos[ing]
his eyes to avoid knowing what was taking place around him." United
States v. Ruhe, 191 F.3d 376, 384 (4th Cir. 1999) (quoting United
States v. Schnabel, 939 F.3d 197, 203 (4th Cir. 1991)). The govern-
ment presented a plethora of evidence that demonstrates that Appel-
lant either knew of the conspiracy, or, at the very least, was willfully
blind to the unlawfulness of his actions.

   Testimony showed that Appellant consistently prescribed large
quantities of opioids despite warning signs that his patients were not
using their medications as prescribed, were seeking his treatment spe-
cifically to obtain drugs, or were drug addicts. See J.A. 177-78, 180-
82, 185, 207-08, 233, 250-51, 253, 350, 353, 359, 390, 392, 518-23,
530-31, 538, 542. Indeed, Appellant continued prescribing medication
to one patient after she repeatedly told him that she could not take it,
J.A. 356; to another after developing sufficient concern that the
patient was selling his medication to contact state officials, J.A. 180-
81; and to yet another after finding a syringe in his possession, J.A.
185. Evidence also revealed instances in which Appellant failed to
conduct even the most basic diagnostic testing before prescribing
opioids. See J.A. 184, 249. Taken together, this evidence supports
                       UNITED STATES v. MCIVER                        21
either of two alternate conclusions: that Appellant had actual knowl-
edge that he was prescribing drugs for non-medical purposes or that
he was willfully blind to his patient’s true motives in seeking his care.
Either circumstance establishes Appellant’s knowledge of the con-
spiracy.

   On this record, we conclude that the government presented suffi-
cient evidence to satisfy both the agreement and knowledge elements
of the conspiracy charge.

  2. Counts 3-5 & 13-15, Unlawful Distribution of a Controlled
     Substance

   Appellant challenges the sufficiency of the evidence on the third
element of the § 841(a)(1) charges, whether he prescribed substances
"outside the usual course of professional practice."16 See Alerre, 430
F.3d at 690 (quoting Moore, 423 U.S. at 124).

   However, the evidence demonstrated that McIver freely distributed
prescriptions for large amounts of controlled substances that are
highly addictive, difficult to obtain, and sought after for nonmedical
purposes. J.A. 134-35, 176, 180-83, 248, 251, 253, 255, 346, 354-56,
388-90, 518-23, 526, 529, 538-40. For one patient, he prescribed
more than 20,000 pills in a single year. J.A. 687. He prescribed drugs
to patients that he either knew or had reason to believe would not take
them as directed. J.A. 354, 356. Some of his patients were drug
addicts who sought treatment from him specifically to obtain con-
trolled substances to use or to sell. J.A. 176, 248, 251, 253, 346, 356,
359. That Appellant knew or suspected his patients of drug abuse is
reflected by the fact that he wrote to state authorities to express con-
cern that his patients might be selling their medications. J.A. 126,
180-81. Appellant exercised minimal medical oversight of his
patients’ dosing practices. J.A. 184, 208, 249, 351, 416-17. He
ignored evidence of the danger of prescribing drugs to certain
patients, the drug-seeking behavior of others, and the drug abuse of
still others. J.A. 177-78, 180-82, 185, 207-08, 233, 250-51, 253, 350,
353, 359, 390, 392, 518-23, 530-31, 538, 542. After several of Appel-
  16
    Appellant does not contest the evidence as to either of the first two
elements.
22                      UNITED STATES v. MCIVER
lant’s patients stopped seeing him, they suffered significant drug
withdrawal effects, at least in one instance requiring hospitalization.
J.A. 211-12, 397. Dr. Storick testified at length about the extent to
which Appellant’s procedures went beyond the parameters of legiti-
mate medical practice. J.A. 523, 527, 533, 542-43.

   This evidence amply supports a finding that McIver’s actions went
beyond the legitimate practice of medicine and were "no different
than [those of] a large-scale pusher," Tran Trong Cuong, 18 F.3d at
1138, and is thus sufficient to support each of McIver’s § 841(a)(1)
convictions.

  3. Counts 11 & 12, Unlawful Distribution of a Controlled
     Substance Resulting in Death

   In order to prove Counts 11 and 12, the government had to estab-
lish that McIver unlawfully distributed drugs to Shealy that resulted
in his death. § 841(b)(1)(C). McIver argues only that the government
did not present sufficient evidence to demonstrate that Shealy died
from the drugs that he prescribed. Again, we disagree.

   Both the pathologist who conducted Shealy’s autopsy and the
forensic toxicologist who examined his bodily fluids testified that
Shealy died as a result of an oxycodone overdose. J.A. 419-20, 427-
30, 456. The pathologist further testified that the amount of oxyco-
done in his system at the time of death was consistent with the
amount prescribed by McIver. J.A. 427-30. This testimony is suffi-
cient to support McIver’s conviction on Counts 11 and 12.

                                   III.

     In light of the foregoing, each of McIver’s convictions is

                                                          AFFIRMED.
