The US Supreme Court [official website] heard oral arguments [day call, PDF] Tuesday in McFadden v. United States [transcript, PDF; JURIST report] to determine what level of knowledge is required for a narcotics conviction. The question originally before the court was whether, to convict a defendant of distribution of a controlled substance analogue, the government must prove that the defendant knew that the substance constituted a controlled substance analogue. A controlled substance analogue is a substance with a chemical structure that is “substantially similar” to a schedule I or II drug and has a “substantially similar” effect on the user. Stephen McFadden was convicted by a jury of nine charges stemming from his distribution of substances that the government alleged were prohibited by the Controlled Substance Analogue Enforcement Act of 1986 [21 USC §§ 802(32)(A), 813], and the US Court of Appeals for the Fourth Circuit affirmed [opinion]. As stated by McFadden’s attorney Tuesday, both parties now agree that “to prove an offense, the government must show that the defendant knowingly distributed an analogue.” However, counsel for McFadden also said Tuesday, “Where we may disagree is over the government’s alternative theory that it can instead show that the defendant knew that the substance was illegal or regulated.” Counsel for the government responded, “Our position is not that we can prevail if we can prove that the defendant believed that his conduct was illegal under some law other than the CSA or the Analogue Act. Our position is that we can prevail if we can prove that a defendant knowingly distributed a drug and that he believed that his conduct, that his distribution of the drug was illegal, generally.”