Congress may prohibit local cultivation and use of marijuana that is permitted under California law. The Commerce Clause grants Congress the authority to regulate purely local activities if those activities are part of an economic class of activities that have a substantial effect on interstate commerce. If Congress decides that the total incidence of a practice poses a threat to a national market, it may regulate the entire class of activities. Given the enforcement difficulties of distinguishing between locally cultivated marijuana and that grown elsewhere, and concerns about diversions of locally cultivated marijuana into illicit channels, Congress had a rational basis for concluding that regulation of local marijuana cultivation and use was necessary to effectuate the national drug laws.