Xiulu Ruan v. United States, 2022 U.S. LEXIS 3089 (S. Ct. June 27, 2022) (Breyer, J.) Justice Breyer delivered the opinion of the Court. A provision of the Controlled Substances Act, codified at 21 U. S. C. §841, makes it a federal crime, “[e]xcept as authorized[,] . . . for any person knowingly or intentionally . . . to manufacture, distribute, or dispense . . . a controlled substance,” such as opioids. 84 Stat. 1260, 21 U. S. C. §841(a) (emphasis added). Registered doctors may prescribe these substances to their patients. But, as provided by regulation, a prescription is only authorized when a doctor issues it “for a legitimate medical purpose . . . acting in the usual course of his professional practice.” 21 CFR §1306.04(a) (2021). In each of these two consolidated cases, a doctor was convicted under §841 for dispensing controlled substances not “as authorized.” The question before us concerns the state of mind that the Government must prove to convict these doctors of violating the statute. We hold that the statute’s “knowingly or intentionally” mens rea applies to authorization. After a defendant produces evidence that he or she was authorized to dispense controlled substances, the Government must prove beyond a reasonable doubt that the defendant knew that he or she was acting in an unauthorized manner, or intended to do so. The question we face concerns §841’s exception from the general prohibition on dispensing controlled substances contained in the phrase “[e]xcept as authorized.” In particular, the question concerns the defendant’s state of mind. To prove that a doctor’s dispensation of drugs via prescription falls within the statute’s prohibition and outside the authorization exception, is it sufficient for the Government to prove that a prescription was in fact not authorized, or must the Government prove that the doctor knew or intended that the prescription was unauthorized? Petitioners Xiulu Ruan and Shakeel Kahn are both doctors who actively practiced medicine. They both possessed licenses permitting them to prescribe controlled substances. The Government separately charged them with unlawfully dispensing and distributing drugs in violation of §841. Each proceeded to a jury trial, and each was convicted of the charges. At their separate trials, Ruan and Kahn argued that their dispensation of drugs was lawful because the drugs were dispensed pursuant to valid prescriptions. As noted above, a regulation provides that, “to be effective,” a prescription “must be issued for a legitimate medical purpose by an individual practitioner acting in the usual course of his professional practice.” 21 CFR §1306.04(a). We assume, as did the courts below and the parties here, that a prescription is “authorized” and therefore lawful if it satisfies this standard. At Ruan’s and Kahn’s trials, the Government argued that the doctors’ prescriptions failed to comply with this standard. The doctors argued that their prescriptions did comply, and that, even if not, the doctors did not knowingly deviate or intentionally deviate from the standard. The Tenth Circuit affirmed Kahn’s convictions. See 989 F. 3d 806, 812, 824-826 (2021). In doing so, the court held that to convict under §841, the Government must prove that a doctor “either: (1) subjectively knew a prescription was issued not for a legitimate medical purpose; or (2) issued a prescription that was objectively not in the usual course of professional practice.” Id., at 825. As §841 makes it unlawful, “[e]xcept as authorized[,] . . . for any person knowingly or intentionally . . . to manufacture, distribute, or dispense . . . a controlled substance.” We now hold that §841’s “knowingly or intentionally” mens rea applies to the “except as authorized” clause. This means that once a defendant meets the burden of producing evidence that his or her conduct was “authorized,” the Government must prove beyond a reasonable doubt that the defendant knowingly or intentionally acted in an unauthorized manner.