Twelve states, mostly in the West, have enacted laws allowing the use of marijuana for medical purposes, and many thousands of patients are seeking relief from a variety of serious illnesses by smoking marijuana or using other herbal cannabis preparations. Meanwhile, the federal Drug Enforcement Administration refuses to recognise these state laws and continues to investigate and arrest, under federal statute, medical marijuana providers and users in those states and elsewhere. Claims and counterclaims about medical marijuana -- much debated by journalists and academics, policymakers at all levels of government, and interested citizens -- include the following: Marijuana is harmful and has no medical value; marijuana effectively treats the symptoms of certain diseases; smoking is an improper route of drug administration; marijuana should be rescheduled to permit medical use; state medical marijuana laws send the wrong message and lead to increased illicit drug use; the medical marijuana movement undermines the war on drugs; patients should not be arrested for using medical marijuana; the federal government should allow the states to experiment and should not interfere with state medical marijuana programs; medical marijuana laws harm the federal drug approval process; the medical cannabis movement is a cynical ploy to legalise marijuana and other drugs. With strong opinions being expressed on all sides of this complex issue, the debate over medical marijuana does not appear to be approaching resolution.