
286 S.E.2d 368 (1982)
STATE of North Carolina
v.
Diane Wilhelmina CHERRY.
No. 813SC777.
Court of Appeals of North Carolina.
February 2, 1982.
*369 Atty. Gen. Rufus L. Edmisten by Asst. Atty. Gen. George W. Boylan, Raleigh, for the State.
Robert L. White, Greenville, for defendant-appellant.
BECTON, Judge.

I
Defendant first argues that the trial court should have allowed her motion to dismiss the bill of indictment. Defendant was originally charged in a Magistrate's Order with feloniously possessing with intent to sell and deliver four grams, but less than fourteen grams, of heroin. Defendant was subsequently indicted for feloniously trafficking in heroin by possessing and transporting 4.6 grams of heroin in violation of G.S. 90-95(h)(4). The "trafficking" offense carries a greater punishment than the offense with which defendant had been originally charged. Defendant contends that the effective date of G.S. 90-95(h)(4) was 1 March 1981, and that, since she is alleged to have committed the crime charged on 3 October 1980, G.S. 90-95(h)(4) "was ex post facto as to her because it expose[d] her to greater punishment and its effective date had not come into being on the date that the crime is alleged to have been committed."
We do not agree. Defendant has misread the applicable statute. As of 3 October 1980, G.S. 90-95(h)(4) provided in pertinent part that

*370 [a]ny person who sells ... transports or possesses four grams or more of ... heroin ... shall be guilty of a felony which felony shall be known as "trafficking in opium or heroin" and if a quantity... involved:
(a) is four grams or more, but less than 14 grams, such person shall, upon conviction, be punished ... for not less than six years nor more than fifteen years ... and shall be fined not less than fifty thousand dollars ($50,000.00).
As of the date of defendant's conviction, 4 March 1981, G.S. 90-95(h)(4) had been amended so that the maximum punishment was a minimum sentence of fourteen years. However, the amendment was applicable only to acts committed on or after 15 April 1981. See G.S. 90-95(h)(4), Editor's notes. Therefore, defendant was not the victim of any ex post facto law or punishment. We also hold that there was no error in superseding the original warrant with the bill of indictment. "The actions of the grand jury are not limited by the charges presented or determined at a probable cause hearing in the district court." State v. McGee, 47 N.C.App. 280, 283, 267 S.E.2d 67, 70, disc. review denied 301 N.C. 101, 273 S.E.2d 306 (1980).

II
Defendant next contends that the trial court erred in denying her motion for a mistrial made when Officer C. E. Weatherington testified, over objection, that the green vegetable material in the cigarettes which the defendant handed to him "contained marijuana." It is not necessary to determine whether Officer Weatherington's formal training with regard to identifying marijuana or his practical experience which resulted in at least 500 first-hand observations of marijuana were sufficient to qualify him as an expert witness because the standard for mistrials under G.S. 15A-1061 is whether the testimony objected to resulted in "substantial and irreparable" prejudice. There was no prejudice in this case to the defendant since (1) the chemist, N. C. Evans, subsequently testified, without objection, that one of the small envelopes submitted to him for analysis by Weatherington contained marijuana, and (2) defendant was charged with trafficking in heroin, not possession of marijuana. Defendant has failed to show that the trial court abused its discretion in denying her motion for a mistrial. See State v. Mills, 39 N.C. App. 47, 249 S.E.2d 446 (1978), disc. review denied 296 N.C. 588, 254 S.E.2d 33 (1979).

III
We find no merit in defendant's next contention that the trial court erred in refusing to order the State to reveal the identity of its confidential informant. The right of a defendant to ascertain the name of an informant is discussed in detail in State v. Ketchie, 286 N.C. 387, 211 S.E.2d 207 (1975) and is further codified in G.S. 15A-978(b). Two things are readily apparent from our case law and statutory law: (1) ordinarily, a defendant is not necessarily entitled to elicit the name of a confidential informant; (2) however, when "the disclosure of the informer's identity, or of the contents of his communication, is relevant and helpful to the defense of the accused, or is essential to fair determination of a cause..." disclosure is required. State v. Moore, 275 N.C. 141, 154, 166 S.E.2d 53, 62-3 (1969) quoting Roviaro v. United States, 353 U.S. 53, 60-61, 77 S.Ct. 623, 628, 1 L.Ed.2d 639, 645 (1957). See also State v. Cameron, 17 N.C.App. 229, 193 S.E.2d 485 (1972), aff'd. 283 N.C. 191, 195 S.E.2d 481 (1973); State v. Johnson, 13 N.C.App. 323, 185 S.E.2d 423 (1971), appeal dismissed 281 N.C. 761, 191 S.E.2d 364 (1972).
In the case before us there is no suggestion that the confidential informant participated in the particular transaction in question. There is no suggestion that the identity of the confidential informant would have in any way been relevant or helpful to the defendant. This assignment of error is overruled.

IV
Defendant also contends that the trial court erred by failing to instruct the jury to *371 disregard a question to which defendant's objection had been sustained.
On cross examination by the district attorney, the following transpired:
Q. And do you know why it is that you have had this reputation all over Greenville for selling dope up and down West Fifth Street?
MR. WHITE: Objection.
THE COURT: Sustained.
MR. WHITE: Request instructions.
THE COURT: Ask your next question.
It would be the better practice for trial courts, upon request, to tell jurors to disregard questions and the suggestions in questions to which objections were sustained. Indeed, as part of its instructions to the jury, either before the evidence or after the evidence, our trial courts may consider giving the following type instruction:
It is the right of counsel to object when testimony or other evidence is offered which he or she believes is not admissible.
When the court sustains an objection to a question, you, the jury, must disregard the question and the answer if one has been given, and draw no inference from the question or answer or speculate as to what the witness would have said if permitted to answer. Evidence stricken from the record must likewise be disregarded. When the Court sustains an objection to any evidence, you, the jury, must disregard such evidence.
When the Court overrules an objection to any evidence, you, the jury, must not give such evidence any more weight than if the objection had not been made.
In this case, however, the trial court's failure to give further elaborating instructions after it had sustained the objection to the question when defendant's counsel said "Request instructions" was not prejudicial error.

V
We have considered defendant's remaining assignments of error relating to the trial court's failure (1) to instruct on the meaning of "transporting" and (2) to grant defendant's motion for a directed verdict, to set the verdict aside, and for a new trial. Simply put, we find no error.
In our view, defendant has been accorded a fair trial, free from prejudicial error.
No error.
CLARK and WHICHARD, JJ., concur.
