The US Supreme Court on Monday rejected a move by two Californian counties to bar patients from using marijuana for medical purposes.
The top court refused to hear a case brought by San Diego and San Bernardo counties that argued the federal law outlawing marijuana should override Californian state law that permits the use, cultivation and possession of the drug for medical purposes.
Twelve other US states have similar laws.
The Californian law, adopted by referendum in 1996, allows chronically ill patients with a medical prescription to use marijuana as a painkiller, providing they are properly registered.
But San Diego and San Bernardo have refused to issue such cards, and an association seeking to promote marijuana use began legal action against them at the end of 2005.
The two counties had argued that allowing marijuana for medical use contradicted the ban on drug use introduced by Congress in 1970.
But they lost twice in lower courts, and then again on appeal in July 2008. The California Supreme Court also refused to take up an appeal, meaning the case is now closed.