                             PUBLISHED

                  UNITED STATES COURT OF APPEALS
                      FOR THE FOURTH CIRCUIT


                            No. 13-4349


UNITED STATES OF AMERICA,

                Plaintiff - Appellee,

           v.

STEPHEN DOMINICK MCFADDEN, a/k/a Stephen Domin McFadden,

                Defendant - Appellant.



Appeal from the United States District Court for the Western
District of Virginia, at Charlottesville. Glen E. Conrad, Chief
District Judge. (3:12-cr-00009-GEC-1)


Argued:   March 19, 2014                  Decided:   May 21, 2014


Before TRAXLER, Chief Judge, and WILKINSON and KEENAN, Circuit
Judges.


Affirmed by published opinion. Judge Keenan wrote the opinion,
in which Chief Judge Traxler and Judge Wilkinson joined.


ARGUED:   J.   Lloyd    Snook,   III,  SNOOK    &   HAUGHEY,   PC,
Charlottesville, Virginia, for Appellant.    Jean Barrett Hudson,
OFFICE OF THE UNITED STATES ATTORNEY, Charlottesville, Virginia,
for Appellee.      ON BRIEF: Timothy J. Heaphy, United States
Attorney, Roanoke, Virginia, Ronald M. Huber, Assistant United
States   Attorney,   OFFICE   OF  THE  UNITED   STATES   ATTORNEY,
Charlottesville, Virginia, for Appellee.
BARBARA MILANO KEENAN, Circuit Judge:

      This   appeal      concerns    a   defendant’s      convictions    involving

the sale of “designer drugs,” in violation of the Controlled

Substance Analogue Enforcement Act of 1986 (the Act), 21 U.S.C.

§§ 802(32)(A), 813.         Stephen D. McFadden was convicted by a jury

of nine charges stemming from his distribution of substances

that the government alleged were prohibited by the Act.                         On

appeal,      McFadden      primarily          asserts     that   the     Act    is

unconstitutionally vague as applied to him, that the district

court     abused   its     discretion     in     making    certain     evidentiary

rulings at trial, and that the government failed to prove that

the   substances      McFadden      distributed     qualified    as     controlled

substance analogues under the Act.                Upon our review, we affirm

the district court’s judgment.



                                         I.

      Before addressing the facts of this case and McFadden’s

challenges to his convictions, we first provide a brief overview

of the Act.        Congress enacted the Act to prevent “underground

chemists” from creating new drugs that have similar effects on

the human body as drugs explicitly prohibited under the federal

drug laws.     See United States v. Klecker, 348 F.3d 69, 70 (4th

Cir. 2003); see also United States v. Hodge, 321 F.3d 429, 432,

437 (3d Cir. 2003) (purpose of the Act is to “make illegal the

                                          2
production    of   designer   drugs   and    other   chemical      variants    of

listed   controlled   substances      that   otherwise    would     escape     the

reach of the drug laws”).          To achieve that purpose, Congress

mandated that a “controlled substance analogue,” when intended

for   human   consumption,    be   treated     under     federal    law   as    a

Schedule I controlled substance.          21 U.S.C. § 813.

      Subject to certain exceptions not at issue in this case, a

“controlled substance analogue” is defined under the Act as:

      a substance-

      (i) the chemical structure of which is substantially
      similar to the chemical structure of a controlled
      substance in schedule I or II;

      (ii)   which   has   a   stimulant,   depressant,   or
      hallucinogenic effect on the central nervous system
      that is substantially similar to or greater than the
      stimulant, depressant, or hallucinogenic effect on the
      central nervous system of a controlled substance in
      schedule I or II; or

      (iii) with respect to a particular person, which such
      person represents or intends to have a stimulant,
      depressant, or hallucinogenic effect on the central
      nervous system that is substantially similar to or
      greater    than   the    stimulant,   depressant,   or
      hallucinogenic effect on the central nervous system of
      a controlled substance in schedule I or II.

21 U.S.C. § 802(32)(A).

      Accordingly, an individual may be convicted for an offense

involving a controlled substance analogue under 21 U.S.C. § 841

if the government establishes that: (1) the alleged analogue

substance has a chemical structure that is substantially similar

to the chemical structure of a controlled substance classified

                                      3
under     Schedule          I    or   Schedule          II   (the     chemical       structure

element); 1 (2) the alleged analogue substance                                  has an actual,

intended       or   claimed        stimulant,           depressant,      or      hallucinogenic

effect    on     the    central        nervous          system    that     is     substantially

similar to or greater than such effect produced by a Schedule I

or    Schedule         II       controlled        substance         (the        pharmacological

similarity element); and (3) the analogue substance is intended

for   human     consumption           (the    human       consumption         element).      See

Klecker, 348 F.3d at 71 (construing 21 U.S.C. §§ 802(32)(A),

813).



                                                  II.

        In July 2011, police investigators in the Charlottesville,

Virginia area began investigating the use and distribution of

certain       synthetic         stimulants        commonly       known     as    “bath   salts.”

When ingested into the human body, bath salts are capable of

producing       similar         effects      as    certain        controlled        substances,

including cocaine, methamphetamine, and methcathinone.

        The    police       investigation          revealed       that     bath     salts   were

being sold from a video rental store in Charlottesville, which

was owned and operated by Lois McDaniel.                                 Using confidential


      1
       Controlled substances are classified under one of five
schedules, which are set forth in 21 U.S.C. § 812 and 21 C.F.R.
§§ 1308.11 through 1308.15.


                                                  4
informants,      investigators   purchased       bath       salts   from    McDaniel,

which later were analyzed by the United States Drug Enforcement

Administration (DEA).          The chemical analysis performed by the

DEA     showed      that      these      bath       salts         contained        3,4-

methylenedioxypyrovalerone                    (MDPV)                and           3,4-

methylenedioxymethcathinone           (methylone,      or    MDMC).        Government

agents later seized from McDaniel’s store additional bath salts

that contained a combination of MDPV, methylone, and 4-methyl-

ethylcathinone (4-MEC).

      McDaniel agreed to cooperate with the investigators, and

informed them that the bath salts she distributed from her store

were supplied by McFadden.              At the investigators’ direction,

McDaniel    initiated        recorded        telephone       conversations        with

McFadden in which she placed orders for bath salts.                              During

these conversations, McFadden discussed the potency and duration

of the “high” experienced by users of the substances he was

distributing.      He also compared the effects of those substances

to    certain     controlled     substances,        including         cocaine      and

methamphetamine.

      As a result of these transactions, investigators received

bath salts supplied by McFadden on five separate occasions.                        The

DEA’s   analysis    showed    that     two    batches       of   these    bath   salts

contained 4-MEC, MDPV, and methylone.                  The three other batches



                                         5
contained    4-MEC,     but     not   MDPV         or   methylone. 2        Based       on   the

findings    of     this    investigation,               the    grand    jury      issued      a

superseding indictment in November 2012, charging McFadden with

nine offenses, including one count of conspiracy to distribute

substances containing the alleged controlled substance analogues

4-MEC, MDPV, and methylone (collectively, the alleged CSAs), and

eight additional counts of distributing these substances. 3

      The   four-day      jury    trial        focused        primarily     on    the    issue

whether     4-MEC,      MDPV,     and      methylone           constitute        controlled

substance    analogues        under      the       Act.       To    prove   the     chemical

structure element, the government presented the testimony of Dr.

Thomas DiBerardino, a chemist employed by the DEA, who qualified

as   an   expert   in     the    field    of       chemical        structures     of    drugs.

      2
       During the course of the government’s investigation, the
DEA, under its emergency temporary scheduling powers in 21
U.S.C. § 811(h), classified MDPV and methylone as Schedule I
controlled substances.   Schedules of Controlled Substances, 76
Fed. Reg. 65371, 65372 (amending 21 C.F.R. § 1308.11) (Oct. 21,
2011). The government did not allege that McFadden distributed
MDPV or methylone after this classification.
      3
       The indictment contained the following charges: conspiracy
to distribute a substance or mixture containing the controlled
substance analogues 4-MEC, MDPV, and methylone, in violation of
21 U.S.C. §§ 841(a)(1), (b)(1)(c) and 846 (Count One); two
counts of distribution of a substance or mixture containing MDPV
and methylone, in violation of 21 U.S.C. §§ 841(a)(1) and
(b)(1)(c) (Counts Two and Three); three counts of distribution
of a substance or mixture containing 4-MEC, MDPV, and methylone,
in violation of 21 U.S.C. §§ 841(a)(1) and (b)(1)(c) (Counts
Four, Five, and Six); and three counts of distribution of a
substance or mixture containing 4-MEC, in violation of 21 U.S.C.
§§ 841(a)(1) and (b)(1)(c) (Counts Seven, Eight, and Nine).


                                               6
Using      chemical    diagrams        as        demonstrative        exhibits,      Dr.

DiBerardino testified that the chemical structures of 4-MEC and

MDPV are each substantially similar to methcathinone, a Schedule

I   controlled   substance.        Dr.          DiBerardino       further   testified,

based on the chemical diagrams, that the chemical structure of

methylone is substantially similar to ecstasy, which also is a

Schedule I controlled substance.

      To   establish     the   pharmacological           similarity       element,   the

government presented the testimony of Dr. Cassandra Prioleau, a

drug science specialist employed by the DEA, who qualified as an

expert in the field of pharmacological effects of drugs.                             Dr.

Prioleau     testified    that    4-MEC         and     MDPV   each   would      have   a

pharmacological        effect     on        the         central     nervous       system

substantially similar to the effect produced by methcathinone.

Dr.   Prioleau   further       testified         that    methylone       would   have   a

substantially     similar      pharmacological            effect    on    the    central

nervous system as ecstasy. 4

      In his defense, McFadden presented the testimony of Dr.

Matthew C. Lee, a primary care physician and pharmacist, who

qualified as an expert in the field of pharmacology and the


      4
       Dr. Prioleau acknowledged during cross-examination that
methylone generally produced only about one-half the stimulant
effect of ecstasy, but also noted that at a “maximum dosage”
level methylone and ecstasy would have equivalent stimulant
effects.


                                            7
effects of medication.               Dr. Lee criticized the methodology used

by Dr. DiBerardino in reaching his conclusions regarding the

chemical structure element, and further stated that MDPV and

methcathinone are not similar in chemical structure. 5                                    Dr. Lee

also       criticized      the    methodology      employed        by       Dr.    Prioleau     in

reaching      her    conclusions        with    respect       to      the    pharmacological

similarity element.               Dr. Lee testified that methylone did not

produce      similar       pharmacological         effects       as    ecstasy,         and    that

there was insufficient scientific data to draw a conclusion that

4-MEC and MDPV produce similar pharmacological effects in humans

as methcathinone.

       After hearing this and other evidence, the jury returned a

verdict       finding      McFadden     guilty       of     each   of       the    nine    counts

alleged       in    the     indictment.         At      a    sentencing           hearing,     the

district       court        found     that     McFadden’s          advisory          sentencing

guidelines         range     was      between      51       months’      and       63     months’

imprisonment.             After considering the factors set forth in 18

U.S.C. § 3553(a), the court imposed a below-guidelines sentence

of     33    months’        imprisonment        for       each     conviction,            to   run

concurrently,         and     a     30-month    period        of      supervised        release.

McFadden filed a timely notice of appeal.

       5
       Dr. Lee did not make an explicit conclusion during his
testimony about whether 4-MEC and methcathinone, or methylone
and ecstasy, were substantially similar in their respective
chemical structures.


                                               8
                                          III.

                                           A.

       We    first   consider      McFadden’s      argument          that       the     Act    is

unconstitutional as applied to him.                    This argument presents the

central      theme   that    the    Act    failed       to     provide      a     person       of

ordinary      intelligence      notice     that    the       conduct       at     issue       was

unlawful.

       McFadden      argues     that       the     Act       fails         to     meet        the

constitutional requirement of notice because: (1) the Act uses a

“standards-based”       scheme,          employing       general       terms          such     as

“substantially       similar”      and    “human     consumption,”              and   lacks     a

list    of    prohibited      substances;        (2)     the    Act    is        subject       to

arbitrary      and   discriminatory         enforcement         in    the        absence       of

statutory      guidance      concerning         prohibited          conduct;          and     (3)

despite      significant      efforts       on     his       part     to        learn       about

prohibited conduct, McFadden was unable to determine “what he

can and cannot do,” and was unaware that the distribution of

controlled substance analogues is prohibited under federal law.

       We review de novo a challenge to the constitutionality of a

federal statute.          United States v. Gibert, 677 F.3d 613, 618

(4th Cir. 2012).            As a general matter, a criminal statute is

unconstitutionally vague if it does not sufficiently define an

offense such that ordinary people can understand what conduct is

prohibited.       Kolender v. Lawson, 461 U.S. 352, 357 (1983).                              This

                                            9
inquiry generally requires an examination of what a person of

“common intelligence” would reasonably understand the statute to

prohibit, rather than what a particular defendant understood the

statute to mean.     See United States v. Washam, 312 F.3d 926, 930

(8th Cir. 2002) (citing United States v. Nat’l Dairy Prods., 372

U.S. 29, 32-33 (1963) and Connally v. Gen. Constr. Co., 269 U.S.

385, 391 (1926)).     Additionally, a statute is unconstitutionally

vague if its definition of the prohibited conduct encourages

arbitrary and discriminatory enforcement.                Kolender, 461 U.S. at

357-58.

     In our decision in Klecker, we rejected a nearly identical

constitutional challenge as that raised by McFadden.                      See 348

F.3d at 71-72.       There, a defendant challenged his convictions

for distributing a chemical compound commonly known as “Foxy.”

Id. at 71.    The government alleged that Foxy was an analogue of

a Schedule 1 controlled substance, diethyltryptamine (DET).                   Id.

at 70.    We held that the Act was not unconstitutionally vague in

its use of the term “substantially similar” with respect to a

defendant    who   lacked   actual    notice      that    a   substance    was    a

controlled substance analogue.            Id. at 72.      We observed that the

considerable similarities, found from a comparison of chemical

diagrams of the alleged analogue substance and the controlled

substance,    were   sufficient      to    “put   a    reasonable    person      on

notice” of Foxy’s composition as a DET analogue.               Id.

                                      10
       This holding in Klecker defeats McFadden’s argument that

the    term   “substantially             similar,”           as       used    in    21     U.S.C.        §

802(32)(A),       is    unconstitutionally                 vague       when     applied         to    the

chemical      compounds         at      issue     here.            The       testimony          of     Dr.

DiBerardino       comprehensively               addressed          the       chemical       diagrams

comparing      the      chemical         structures          of       4-MEC     and      MDPV        with

methcathinone, and methylone with ecstasy.

       Presenting two-dimensional diagrams in which the chemical

structures of 4-MEC and MDPV were displayed in an overlapping

manner     with      the     chemical         structure            of       methcathinone,            Dr.

DiBerardino       explained           that      these        substances            share        a    core

chemical      structure,             namely        that       of        a     compound              called

phenethylamine.            Although the overlapping diagrams showed that

the    substances          each      have       some       unique        features          in        their

respective chemical compositions, Dr. DiBerardino testified that

these unique features do not affect the chemical core of the

substances.       Rather, he stated that the diagrams reflected that

“[e]verything          that’s     different           is    on     the       periphery”         of     the

respective chemical structures.                       Dr. DiBerardino made the same

type     of   comparison             examining         the        chemical         structures           of

methylone     and      ecstasy,         during     which         he     explained        that        those

substances        share           the       same           core         chemical         structure,

phenethylamine,          and      that    the      structural            differences            between

methylone and ecstasy are insignificant.

                                                 11
       Based on his evaluation of these diagrams of the chemical

compounds      at     issue,        Dr.     DiBerardino        concluded          that    the

controlled      substances       and       the     respective     alleged        CSAs    have

substantially         similar        chemical          structures.               Thus,     Dr.

DiBerardino applied the statutory term “substantially similar”

in evaluating the core chemical structures of the substances at

issue,   and    was    able    to    distinguish         the   differences         in    those

structures as peripheral and inconsequential.                           After reviewing

these    chemical     diagrams,        we    agree      with   the     district        court’s

conclusion that for purposes of satisfying the constitutional

requirement of notice, there are substantial similarities in the

chemical      structures        between          the    alleged      CSAs        and     their

controlled substance counterparts.

       We also view the chemical diagrams and Dr. DiBerardino’s

testimony in light of the evidence concerning McFadden’s intent

that    the    alleged    CSAs      be      consumed      by   humans       to    produce   a

stimulant effect.         See Klecker, 348 F.3d at 72 (observing that

defendant’s      intent    that      Foxy        be    ingested   as    a    hallucinogen

reinforced the conclusion that the defendant had adequate notice

that Foxy would be regarded as a DET analogue).                                   As stated

above,    McFadden       informed         McDaniel      during    recorded        telephone

conversations that the substances he was distributing produced




                                              12
effects similar to certain controlled substances. 6                           The fact that

McFadden intended that the substances he was distributing be

used       as      alternatives        to      controlled            substances          further

demonstrates        that     a   reasonable           person    in    his    position      would

understand that his conduct was prohibited by the Act.                                   See id.

In view of this evidence, the district court did not err in

concluding that the statutory term “substantially similar,” as

applied here, would put a reasonable person on notice concerning

the proscribed conduct.

       We       further    disagree     with          McFadden’s      argument      that     the

statutory term “human consumption” is unconstitutionally vague.

See 21 U.S.C. § 813.                  Although McFadden notes correctly that

this term is not defined in the Act, the lack of a statutory

definition does not render the Act unconstitutional per se.                                  See

Chapman      v.    United    States,        500       U.S.    453,    462,   467-68       (1991)

(holding that 21 U.S.C. § 841(b)(1)(B) is not unconstitutionally

vague       despite       lack   of    statutory             definition      of    the     terms

“mixture”         and   “substance”).             A    statute       need    not   contain     a

definition of every term within its text, and, in the absence of

a statutory definition, courts will give terms their ordinary



       6
       As discussed later in this opinion, we disagree with
McFadden’s argument that the district court erred in admitting
the recorded telephone conversations into evidence.  See infra
at 20-21.


                                              13
meaning.     See United States v. Day, 700 F.3d 713, 725 (4th Cir.

2012) (citing Chapman, 500 U.S. at 462, 467-68).

       We agree with the district court that, in the context of

the Act, the ordinary meaning of the term “human consumption”

plainly encompasses the use of a substance by a human being in a

manner that introduces the substance into the body.                        See Black’s

Law Dictionary 359 (9th ed. 2009) (defining “consumption” as

“the use of a thing in a way that exhausts it”).                       We therefore

conclude that there is no ambiguity or vagueness in the Act’s

use of the term “human consumption.”

       Additionally, we reject McFadden’s argument that the Act is

unconstitutionally vague because it does not provide a list of

substances        that    qualify     as    controlled      substance       analogues.

Because     the     Act    provides       for    the   comparison     of     different

chemical compounds to determine whether they are “substantially

similar,”    a     list    of    particular      chemical      compounds    could    not

encapsulate the variety of substances potentially covered by the

Act.      Moreover,       such   a   requirement       would    undermine    the    very

purpose    of     the     Act,    which    is    to    prevent    individuals       from

creating    slightly       modified       versions     of   controlled      substances

that produce similar effects and entail similar dangers as those

controlled substances.            See Klecker, 348 F.3d at 70; Hodge, 321

F.3d at 432, 437.



                                            14
       Given    the     creativity      of   individuals         manufacturing        these

analogue substances, see United States v. Hofstatter, 8 F.3d

316, 322 (6th Cir. 1993), there is genuine potential that the

creation       of     such    substances       could     outpace    any     efforts      by

authorities to identify and catalog them.                        Thus, we decline to

extend    our       holding    in    Klecker      by   imposing     a    constitutional

notice requirement that the Act contain a list of prohibited

substances.          See United States v. Fisher, 289 F.3d 1329, 1337

n.11 (11th Cir. 2002) (rejecting vagueness challenge and noting

that     “[n]o        list     of     controlled        substance        analogues       is

necessary”).

       We also find no merit in McFadden’s argument that the Act

is subject to arbitrary and discriminatory enforcement.                           We held

in Klecker that the Act’s “intent requirement alone tends to

defeat    any       vagueness       challenge     based    on    the     potential      for

arbitrary enforcement.”              348 F.3d at 71.          We explained that this

intent    element       requires      that   the       government       prove    that   the

defendant meant for the substance at issue to be consumed by

humans.      Id.; see also United States v. Roberts, 363 F.3d 118,

126    (2d     Cir.    2004)    (holding        that    the     “intended       for   human

consumption”         element    protects     against      arbitrary       enforcement).

Arbitrary and discriminatory enforcement further is prevented by

the additional statutory requirements that the government prove

(1) substantial chemical similarity between the alleged analogue

                                             15
substance      and    the     controlled        substance,          and     (2)     actual,

intended, or claimed pharmacological similarity of the alleged

analogue substance and the controlled substance.                            See Klecker,

348 F.3d at 71.             Accordingly, we reject McFadden’s arguments

that   the    Act    failed    to    provide     him    adequate          notice    of    the

prohibited      conduct        and     was      subject        to     arbitrary           and

discriminatory enforcement.

       We likewise find no merit in McFadden’s argument that the

Act is unconstitutional as applied because he “took reasonable

steps to inform himself as to the legality of the chemicals that

he was selling,” and did not find any information indicating

that his actions were illegal.                  In support of this argument,

McFadden relies on the fact that he visited the DEA’s website to

determine whether the substances at issue were prohibited, but

that he did not see the disclaimers on the website discussing

the Act and controlled substance analogues.

       McFadden’s     argument       fails     because    it    flouts        the     well-

settled    general     principle      that     “ignorance      of     the     law    is    no

excuse.”      See United States v. Mitchell, 209 F.3d 319, 323 (4th

Cir. 2000) (citation omitted).                 Moreover, McFadden provides no

authority supporting his novel proposition that we should depart

from   this    general      rule     because    he     unsuccessfully         sought      to

determine     whether    his       conduct     was   lawful.         Accordingly,          we

reject    McFadden’s     argument       that    the     Act    is    unconstitutional

                                          16
because he lacked notice that the distribution of controlled

substance analogues is prohibited under federal law.

                                          B.

       We     next   address      McFadden’s   arguments    concerning     certain

rulings made by the district court during the trial.                       McFadden

contends that the district court erred: (1) in permitting the

testimony of Toby Sykes, an individual who purchased bath salts

from       McDaniel;   (2)   in    admitting   into    evidence    recordings     of

McFadden’s      telephone      conversations    with    McDaniel;    and    (3)   in

declining to instruct the jury that the government was required

to prove that McFadden effectively knew that the substances at

issue had the essential characteristics of controlled substance

analogues.

                                          1.

       The     government      offered   the   testimony    of    Toby   Sykes    as

evidence       supporting      the    pharmacological      similarity      element.

Sykes testified that he was a former methamphetamine addict who

purchased bath salts from McDaniel, and that his use of these

bath salts produced a far more potent effect on his body than

his use of methamphetamine. 7


       7
       Although Sykes compared the bath salts to methamphetamine
rather than methcathinone, Dr. Prioleau testified that various
studies showed that MDPV and methylone produce a similar
pharmacological effect in laboratory animals as the effect
generated by methamphetamine.     Accordingly, as the district
(Continued)
                                          17
        McFadden     objected         to   Sykes’      testimony         on   the   ground    of

relevance, because it was uncertain whether the bath salts that

Sykes consumed had been supplied by McFadden or were in the same

form and doses as those delivered to McDaniel.                                  The district

court    overruled        McFadden’s       objection,         but       granted     him    “great

latitude”     to    cross-examine          Sykes      concerning          whether     he    could

state    that      the    substances        he     purchased        were      distributed     by

McFadden. 8

      We review for abuse of discretion a district court’s ruling

concerning       the     admissibility        of      evidence.          United     States    v.

Summers, 666 F.3d 192, 197 (4th Cir. 2011).                              Under Rule 402 of

the   Federal       Rules        of   Evidence,        all    “relevant”          evidence    is

admissible unless specifically prohibited by the Constitution, a

federal    statute,         or    another      evidentiary          rule.         Evidence    is

relevant if it has a tendency to make a fact pertinent to the

case “more or less probable than [the fact] would be without the

evidence.”       Fed R. Evid. 401; United States v. Powers, 59 F.3d

1460,     1465     (4th     Cir.      1995).          We     have       observed     that    the

determination          of    relevance           “presents          a     low     barrier     to



court   found,   Sykes’  comparison   of   the   bath  salts  to
methamphetamine was consistent with Dr. Prioleau’s testimony.
     8
       On appeal, McFadden bases his argument concerning Sykes’
testimony on relevancy grounds, and does not argue that the
testimony should have been struck under Federal Rule of Evidence
403 as having a probative value substantially outweighed by the
danger of unfair prejudice.


                                                 18
admissibility,”              and     that     evidence             need     only     be     “worth

consideration by the jury” to be admissible.                                 United States v.

Leftenant, 341 F.3d 338, 346 (4th Cir. 2003) (citation omitted).

Accordingly,            a     district       court           has    broad       discretion       in

determining whether certain evidence is relevant.                                  United States

v. Queen, 132 F.3d 991, 998 (4th Cir. 1997).

       Applying this deferential standard of review, we conclude

that       the    district         court    did        not    abuse       its    discretion      in

admitting Sykes’ testimony.                       As McFadden concedes, there was

some overlap between the period in which Sykes purchased bath

salts from McDaniel and the period in which McFadden supplied

McDaniel         with       such    substances.              Also,        importantly,      Sykes’

description of the packaging of the bath salts he purchased from

McDaniel         matched      the    description             of    the     packaging      used   by

McFadden         in   distributing          the    substances.               Sykes    was   shown

several exhibits of “blue baggies” containing substances that

the government agents had purchased from McDaniel and, on at

least one occasion, directly from McFadden.                                     Sykes testified

that he recognized the packaging of those exhibits because he

had purchased bath salts from McDaniel in similar blue baggies. 9



       9
        McDaniel was also shown these exhibits during her
testimony, during which she stated that she recognized those
items as originating from McFadden because of their distinctive
packaging.


                                                  19
      Given this foundation evidence tending to show that some of

the   bath    salts      consumed    by    Sykes     were   supplied     by   McFadden,

Sykes’ testimony concerning the bath salts’ effect on his body

properly was submitted to the jury for purposes of establishing

the   pharmacological           similarity    element.       Although      there      were

flaws in Sykes’ testimony relating to the time period at issue

and whether McDaniel altered the substances after receiving them

from McFadden, such flaws were explored during cross-examination

and were relevant to the weight to be given Sykes’ testimony,

not to its admissibility.             See Ziskie v. Mineta, 547 F.3d 220,

225   (4th    Cir.      2008)    (noting     that    determining     the      weight    of

evidence entails a different inquiry than the relevance inquiry

required by Rules 401 and 402 of the Federal Rules of Evidence).

                                             2.

      We next consider McFadden’s challenge to the admission of

evidence     of     recorded     telephone        conversations     between     him    and

McDaniel.         In    the    district    court,     McFadden    objected      to    this

evidence on the ground that the comparisons he made during these

conversations were irrelevant to the crimes charged, because he

claimed      that      4-MEC    produced     effects    similar     to   cocaine       and

methamphetamine, controlled substances not used for comparison

under   the       chemical      structure     element.        The    district        court

overruled McFadden’s objection, finding that this evidence was



                                             20
relevant to both the pharmacological similarity element and the

human consumption element.

      On appeal, McFadden argues solely that the district court

erred in concluding that the recordings were relevant to the

pharmacological similarity element.               McFadden does not address

the district court’s separate conclusion that this evidence was

relevant to the human consumption element, nor does he raise an

argument that admission of this evidence was unduly prejudicial

under Rule 403.         Because the human consumption element was an

independent basis for the district court’s admission of this

evidence, we affirm the court’s ruling on that basis and do not

address McFadden’s argument whether the recordings were relevant

to proof of the pharmacological similarity element.                   See United

States   v.     Hatchett,   245   F.3d     625,    644-45    (7th     Cir.   2001)

(holding defendant waived argument concerning district court’s

ruling on admissibility of evidence by failing to challenge on

appeal one of two independent grounds for court’s ruling).

                                      3.

      McFadden    next    asserts,    on    the    basis    of   out-of-circuit

precedent, that the district court erred in refusing to instruct

the jury that the government was required to prove that he knew,

had a strong suspicion, or deliberately avoided knowledge that

the   alleged    CSAs    possessed   the   characteristics       of    controlled

substance analogues.         See United States v. Turcotte, 405 F.3d

                                      21
515, 527 (7th Cir. 2005).                 We review for abuse of discretion the

district court’s denial of the requested instruction.                                          United

States v. Bartko, 728 F.3d 327, 343 (4th Cir. 2013).                                    To show an

abuse    of    discretion,          a     defendant          must      establish         that     the

proffered       instruction:             “(1)         was       correct,         (2)     was      not

substantially        covered        by   the     charge         that   the       district       court

actually      gave    to     the    jury,       and       (3)    involved        some    point       so

important that the failure to give the instruction seriously

impaired the defendant’s defense.”                        Id.

       McFadden’s argument fails at the outset because he cannot

satisfy the first requirement of this test.                               The instruction he

proposed is not a correct statement of the law in this Circuit.

In Klecker, we set forth the elements that the government was

required      to     prove     to       obtain        a     conviction       under       the     Act,

including the scienter requirement that the defendant intended

that the substance at issue be consumed by humans.                                     348 F.3d at

71.     We    further        stated      that     the        Act    may     be    applied       to    a

defendant who lacks actual notice that the substance at issue

could be a controlled substance analogue.                           Id. at 72.

       In contrast to our decision in Klecker, the Seventh Circuit

has imposed a strict knowledge requirement before a defendant

may be convicted of violating the Act.                                 In its decision in

Turcotte, the court stated that “our precedents demand a showing

that    the    defendant        knew      the         substance        in    question       was      a

                                                 22
controlled substance analogue.”                    405 F.3d at 527.           Because we

have   not   imposed        such   a    knowledge      requirement,      and    have   not

included     the      concepts     of    “strong       suspicion”      or    “deliberate

avoidance” in framing the scienter requirement under the Act, we

hold    that        the     district     court       properly       denied     McFadden’s

requested jury instruction.

                                              C.

       Finally,      we     address     McFadden’s      argument      challenging      the

sufficiency of the evidence and the district court’s denial of

his motion for judgment of acquittal.                        McFadden’s sufficiency

argument is limited to his contention that the government failed

to satisfy its evidentiary burden of demonstrating that 4-MEC,

MDPV, and methylone qualify as controlled substance analogues.

McFadden     does     not    otherwise     contest      the     jury’s      verdict    with

respect to the conspiracy offense and the substantive counts of

distributing controlled substance analogues in violation of the

Act.

       We review de novo the district court’s denial of a motion

for judgment of acquittal.               United States v. Hamilton, 699 F.3d

356, 361 (4th Cir. 2012).               In considering a defendant’s argument

that the evidence was insufficient to support his convictions,

we will uphold a jury’s verdict if, viewing the evidence in the

light most favorable to the government, there is substantial

evidence       in     the     record     to        support    the     verdict.          Id.

                                              23
“Substantial evidence” is “evidence that a reasonable finder of

fact       could    accept     as     adequate          and    sufficient         to    support        a

conclusion of a defendant’s guilt beyond a reasonable doubt.”

United States v. Green, 599 F.3d 360, 367 (4th Cir. 2010).

       In conducting this review, we afford the jury’s verdict

deference          because     “it    is   the      jury’s          province      to    weigh        the

credibility of the witnesses, and to resolve any conflicts in

the evidence.”           United States v. Dinkins, 691 F.3d 358, 387 (4th

Cir.       2012)     (citation        omitted).               Accordingly,          a     defendant

challenging the sufficiency of the evidence on appeal bears a

“heavy       burden,”         and     we      will        reverse          a    conviction           for

insufficient          evidence        “only         in     the       rare       case    when         the

prosecution’s failure is clear.”                          Hamilton, 699 F.3d at 361-62

(citation and internal quotation marks omitted).

       For     ease      of    review,        we        restate      the       elements       of     the

distribution         offenses        for   which         McFadden        was    convicted.            In

addition to proving that McFadden distributed the substances at

issue,       the     government         was        required         to     prove       that        those

substances: (1) have a substantially similar chemical structure

as     a    Schedule      I    or     II   controlled             substance;        (2)       have     a

substantially similar or greater pharmacological effect on the

human central nervous system as a Schedule I or II controlled

substance,          which      effect      was          either      actual,        intended,          or

represented         by   the    defendant;          and       (3)    were      intended       by     the

                                                   24
defendant to be consumed by humans.                   See Klecker, 348 F.3d at

71.

       As stated above, the government presented the testimony of

Dr.    DiBerardino,          who     concluded     that    4-MEC    and    MDPV    are

substantially similar in chemical structure as methcathinone, a

Schedule I controlled substance.                  The government also presented

the testimony of Dr. Prioleau, who concluded that 4-MEC and MDPV

produce    a    substantially          similar      pharmacological       effect    as

methcathinone.       McFadden asks us to cast aside Dr. DiBerardino

and Dr. Prioleau’s opinions and adopt the conflicting views of

McFadden’s expert witness, Dr. Lee.                   According to Dr. Lee, the

scientific methods employed by Dr. DiBerardino and Dr. Prioleau

were    inadequate      to    reach     their     respective    conclusions,       with

which Dr. Lee disagreed.

       We recognized long ago that “[a]n appellate court is not

the    proper   forum    to        refight   a    battle   of   expert    witnesses.”

Connorton v. Harbor Towing Corp., 352 F.2d 517, 518 (4th Cir.

1965) (per curiam), quoted in United States v. Wood, 741 F.3d

417, 425 (4th Cir. 2013).              That fight was waged in the district

court in this case, and the jury chose to accept the conclusions

of Dr. DiBerardino and Dr. Prioleau, despite defense counsel’s

vigorous cross-examination of those witnesses and the opposing

testimony of Dr. Lee.



                                             25
       It     would   be     improper    under      our     standard      of    review    to

elevate Dr. Lee’s opinion over the opinions of Dr. DiBerardino

and Dr. Prioleau, because it is the jury’s function to weigh

witnesses’ credibility, to determine the weight to be accorded

their       testimony,     and   to    resolve      conflicts       in    the     evidence.

Dinkins, 691 F.3d at 387; United States v. Maceo, 873 F.2d 1, 7

(4th Cir. 1989).             Therefore, based on the record before us, we

conclude that the government presented sufficient evidence that

4-MEC and MDPV are substantially similar in chemical structure

as methcathinone, a Schedule 1 substance.                         We further conclude

that the government presented sufficient evidence that 4-MEC and

MDPV    produce       actual     pharmacological          effects    on     the    central

nervous system substantially similar to the effects produced by

methcathinone. 10        In light of this conclusion concerning “actual”

pharmacological          similarity,      we       need    not    address       McFadden’s

argument that there was insufficient proof that he “represented

or     intended”      that     4-MEC    and    MDPV       would   have    substantially

similar pharmacological effects as a controlled substance. 11                            See


       10
       We note that because the jury’s verdict is well-supported
by Dr. DiBerardino and Dr. Prioleau’s testimony, we need not
consider Sykes’ testimony in determining whether the government
proved actual pharmacological similarity of these substances at
issue.
       11
         We therefore need not reach McFadden’s arguments
concerning his statements to McDaniel that 4-MEC and mixtures
containing 4-MEC have an effect similar to substances other than
(Continued)
                                              26
Klecker,       348     F.3d    at   71   (government         may    establish        the

pharmacological similarity element by showing “actual, intended,

or claimed” similarity) (emphasis added).

       Having reached this conclusion with respect to 4-MEC and

MDPV, we need not address whether there was sufficient evidence

in     the    record    to    conclude   that      methylone       qualified    as    a

controlled      substance      analogue.       Each     of   the   charges     in    the

superseding indictment relating to methylone also alleged in the

conjunctive that McFadden distributed MDPV or 4-MEC with respect

to those counts.         In other words, none of the charges hinged on

a finding that methylone qualified as a controlled substance

analogue. 12         Accordingly,   even      if   we   agreed     with   McFadden’s

arguments relating to methylone, we nevertheless would affirm

each of his convictions.            See Turner v. United States, 396 U.S.

398,    420    (1970)     (reaffirming     the     general     rule    that    if    an

indictment charges several acts in the conjunctive, a guilty

verdict stands if the evidence is sufficient with respect to any

one of the acts); United States v. Bollin, 264 F.3d 391, 412



methcathinone, and do not decide whether the pharmacological
similarity element may be established by comparing the alleged
analogue substance to a different controlled substance than used
for comparison under the chemical structure element.
     12
        We further observe that because the government agreed to
remove methylone from the calculation of drug weight for
purposes    of   determining   McFadden’s   advisory  sentencing
guidelines range, methylone was not a factor in the court’s
determination of McFadden’s sentence.


                                         27
n.14   (4th    Cir.    2001)    (in   case    involving       perjury    allegation

charged   in    the    conjunctive     pertaining        to    two   alleged   false

statements,     holding        that   Court    need      not     reach   arguments

pertaining to the first alleged false statement because evidence

supported     jury    verdict    relating     to   the    second     alleged   false

statement).



                                       IV.

       For these reasons, we affirm the district court’s judgment.



                                                                           AFFIRMED




                                        28
