On May 14, 2001, the U.S. Supreme Court ruled 8 to 0 in United States vs. Oakland Cannabis Buyers' Cooperative that the cooperatives permitted under California law to sell marijuana to medical patients who had a physician's approval to use the drug were unconstitutional under federal law.

One of the justices, Stephen G. Breyer, declined to rule on the case because his brother, a U.S. district judge, had issued two of the original rulings that barred California cannabis buyers' cooperatives from distributing marijuana. These rulings started the chain of events that brought the case to the Supreme Court.

The justices engaged in an often-spirited debate about whether or not marijuana was an effective treatment for certain diseases and conditions. They declined, however, to consider the validity of "medical marijuana" arguments, deciding instead to interpret the narrow question they had been given: Does the Controlled Substances Act...