To ensure that seriously ill Californians have the right to obtain and use marijuana for medical purposes, California passed Proposition 215, the “Medical Use of Marijuana” initiative in 1996. Proposition 215 was codified into law as the “Compassionate Use Act.” However, in 2001, in United States versus Oakland Cannabis Buyers’ Cooperative the Supreme Court held that there is no medical exception to the Controlled Substances Act’s (CSA) prohibitions on manufacturing and distributing marijuana. In reviewing Proposition 215 and the CSA, factual and procedural history, opinion summaries, and legal analysis, this paper examines the constitutionality of the CSA as applied to medical marijuana which was necessary to adequately decide the Oakland case, as well as an examination of the fundamental principles of federalism. A constitutional inquiry is necessary to remain consistent with the Rehnquist Court’s recent efforts to reestablish federalism and to rein in Congress’s abuse of its commerce power. A determination that the Federal Government cannot regulate such intrastate activity related to medical use of marijuana, when California’s State laws sanction and regulate it, would not compromise existing Federal drug laws. It would only require that Congress act within its constitutional authority.