Nearly a quarter of cancer patients treated through the Seattle Cancer Care Alliance used cannabis within the past year, according to a recent study. Survey participants said they used marijuana to relieve cancer symptoms and treatment side effects, including pain, nausea and loss of appetite, as well as to improve their mood and help them sleep.

The survey respondents, whose average age was 58, were several times more likely to use cannabis than their peers in the general population.

Washington is one of eight states that allow recreational marijuana use, and more than half of states permit medical use of cannabis or its non-psychoactive component cannabidiol. A majority of the respondents said legalization made them more likely to use cannabis.

Federal restrictions limit studies of medical marijuana, but a recent research review by the National Academies of Sciences, Engineering and Medicine concluded that cannabis and its chemical components can reduce chronic pain and help manage chemotherapy-induced nausea.

A quick web search reveals countless endorsements of cannabis as a cancer cure. But although some studies show that cannabis slows the growth of cancer cells in test tubes and in mice, it has not been proved as a cancer treatment in clinical trials.

In November, the Food and Drug Administration cracked down on overblown cancer cure claims. Four companies received warning letters for the online sale of cannabidiol oil, candies and other products that purport to prevent, treat or cure cancer. The agency fears such claims could steer patients away from conventional medical treatments backed by more research.