They are Californians who suffer from a brain tumor and a degenerative spinal disease, respectively. [Angel Raich] and [Diane Monson] have testified that marijuana eases pain and helps them function in ways that other drugs do not. Most medical researchers find that plausible, as did 56% of California voters when they approved Proposition 215 legalizing medical marijuana in 1996.
Yet, as Justice Sandra Day O'Connor noted in her dissent, the government "has not overcome empirical doubt that the number of Californians engaged in personal cultivation, possession, and use of medical marijuana, or the amount of marijuana they produce, is enough to threaten the federal regime." As important, she wrote, it's not even clear that medical marijuana is commerce as we normally understand the term.
Indeed, in her opinion, O'Connor stressed that having states experimenting with state medical marijuana laws "exemplifies the role of states as laboratories" of democracy. According to the majority, though, such experiments are forbidden when it comes to medical marijuana that never leaves California or is never bought or sold.