SAN FRANCISCO — A California woman whose doctor says marijuana is the only medicine keeping her alive can face federal prosecution on drug charges, a U.S. appeals court ruled yesterday.

The case was brought by Angel Raich, an Oakland mother of two who suffers from scoliosis, a brain tumor, chronic nausea, and other ailments. On her doctor’s advice, she eats or smokes marijuana every couple of hours to ease her pain and bolster a nonexistent appetite as conventional drugs did not work.

The Supreme Court ruled against Ms. Raich two years ago, saying that medical marijuana users and their suppliers could be prosecuted for breaching federal drug laws even if they lived in a state such as California where medical pot is legal. Because of that ruling, the issue before the 9th U.S. Circuit Court of Appeals was narrowed to the so-called right-to-life theory: that marijuana should be allowed if it is the only viable option to keep a patient alive.

Ms. Raich, 41, sobbed when she was told of the decision and said she would continue using the drug.

“I’m sure not going to let them kill me,” she said. “Oh, my God.”

Although the three-judge appeals panel refused Ms. Raich’s request to block enforcement of the 1970 Controlled Substances Act, it left open the possibility that if she were arrested and prosecuted, she might be able to argue that she possessed marijuana as a last resort to stay alive, in what is known as a “medical necessity defense.”

“I have to get myself busted in order to try to save my life,” Ms. Raich said.