The Marijuana Policy Project releases a wonderfully detailed report on the state of state marijuana laws. The study is called State-by-State Medical Marijuana Laws: How to Remove the Threat of Arrest. An encouraging excerpt from the press release.
Nine states—Alaska, California, Colorado, Hawaii, Maine, Nevada, Oregon, Vermont, and Washington—have laws that effectively protect medical marijuana patients from arrest. A Maryland law enacted in 2003 protects patients from the threat of jail but does not provide protection from arrest.
The federal government cannot nullify state medical marijuana laws, and recent federal court decisions have confirmed that states may enact such laws. In Conant v. Walters, a federal appeals court upheld doctors' right to recommend marijuana pursuant to such laws, and the U.S. Supreme Court declined to hear the government's appeal. Because 99 percent of all marijuana arrests are made by state and local officials, these laws provide substantial protection for patients, despite federal hostility.
State laws have worked smoothly and increased in popularity. Maine's law has been so uncontroversial that in 2002 a bill doubling the amount of marijuana that patients may possess passed the state Senate on a voice vote, becoming law with no organized opposition. A recent statewide California poll showed 74 percent support for the state's medical marijuana law—up from the 56 percent who voted for it in 1996.