The defendant was convicted of operating a motor vehicle while under the influence of narcotic drugs[*49] (G. L. c. 90, § 24 [1988 ed.]). The evidence warranted a finding that, before his arrest, the defendant had consumed codeine for which he had a prescription. Chapter 90, § 24 (l)(a)(l), of the General Laws makes it an offense to operate a motor vehicle while under the influence of “narcotic drugs . . . as defined in [G. L. c. 94C, § l].”^[1] There was no direct evidence that codeine is a narcotic drug as defined in G. L. c. 94C, § 1.

The defendant moved for a required finding of not guilty. The trial judge denied the motion, erroneously ruling that “the law states that prescription drugs are narcotics.” On appeal, the Appeals Court concluded, on different grounds, that the evidence was sufficient to warrant a guilty finding, but ordered a new trial because of reversible error on issues we need not consider. Commonwealth v. Green, 27 Mass. App. Ct. 762, 765, 711 (1989). That court concluded that codeine is a derivative of opium, and therefore is within the definition of a narcotic drug in G. L. c. 94C, § 1. It regarded the evidence as sufficient on two grounds: (1) a reading of G. L. c. 94C in its entirety, not just § 1 of that chapter, shows that in G L. c 94C the Legislature treated codeine as a narcotic drug {id. at 765-767), and (2) a judge may appropriately take judicial notice that codeine is a derivative of opium and thus is a narcotic drug as defined in § 1 {id. at 767-769).

[*50] We agree with the Appeals Court that the trial judge could have taken judicial notice that codeine is a derivative of opium,^[2] but he did not take judicial notice of that fact, even when requested to do so. It is inappropriate to supply an essential element of proof by taking judicial notice of a fact at the appellate level. See Commonwealth v. Kingsbury, 378 Mass. 751, 755 (1979) (“We would not supplement the Commonwealth’s proof on appeal by taking judicial notice of a fact not submitted to the jury”). We thus conclude that proof that codeine is derivative of opium was not made at trial and may not now be made by the taking of judicial notice by this court.

Consequently, the evidence was sufficient to warrant the defendant’s conviction only if, as a matter of law, G. L. c. 94C, § 1, includes codeine within the definition of “narcotic drugs.” Section 1 defines a “narcotic drug” to include derivatives of opium, but it says nothing about codeine itself. Section 24 (l)(a)(l) of G. L. c. 90 directs us only to the definition of “narcotic drug” in § 1 of G. L. c. 94C, not to all of G. L. c. 94C. Consideration of the status of codeine in G. L. c. 94C as a whole would be contrary to the explicit direction of G. L. c. 90, § 24 (l)(a)(l), and inconsistent with this court’s traditional policy that we construe criminal statutes narrowly against the Commonwealth. See Commonwealth v. Marrone, 387 Mass. 702, 706 (1982); Commonwealth v. Clinton, 374 Mass. 719, 721 (1978), and cases cited.^[3] Because the evidence did not show that codeine is a narcotic drug as defined in G. L. c. 94C, § 1, and because § 1 does not make it so by its terms, the defendant’s motion for a required finding of not guilty should have been allowed. The Commonwealth could have easily met its burden of[*51] proof that codeine was a derivative of opium by presenting expert testimony.

The judgment is reversed. The verdict is set aside. Judgment shall be entered for the defendant.

So ordered.