The split three-judge opinion from Judge Harry Pregerson expressed sympathy for some arguments by plaintiff Angel Raich, 41, an Oakland resident whose doctor testified she could die if she stopped smoking pot. But the ruling backed the 1970 federal Controlled Substances Act barring marijuana.

Raich, who suffers from many ailments, says marijuana keeps her alive by easing pain and bolstering appetite.

"Today I found out I am basically a dead man walking," Raich, who once worked as an accountant and massage therapist, told Reuters. "Today the court said I don't have the constitutional right to basically stay alive."

The mother of two said U.S. officials had never moved to arrest her or bar her from using marijuana and said she would continue to do so every two hours. "I'm damned if I do, damned if I don't," she said.

Raich said she would lobby Congress in Washington to change U.S. law. The court said use of the drug for medical purposes was gaining support but federal law still banned it.

"We agree with Raich that medical and conventional wisdom that recognizes the use of marijuana for medical purposes is gaining traction in the law as well," the judge wrote.

The ruling acknowledged the law could change if legislators reconsider the issue.

"Although that day has not yet dawned, considering that during the last 10 years 11 states have legalized the use of medical marijuana, that day may be upon on us sooner than expected," Pregerson said.

Voters in California, the nation's most populous state, became the first to approve medical marijuana in 1996, putting it in direct conflict with federal law. Gov. Arnold Schwarzenegger has admitting using marijuana in the past.