A Northern California cancer patient died from a rare fungal infection, and doctors are now questioning whether medical marijuana was the source.

The investigation started after a couple young men who were undergoing chemotherapy and stem cell therapy at UC Davis Cancer Center both developed dangerous infections caused by the same fungus, doctors told CBS San Francisco.

After one of the men died, doctors started trying to track down how they’d been exposed to the fungus. And CBS reports they found that both patients had been using medical marijuana to combat nausea from their cancer treatments.

The UC Davis doctors partnered with Steep Hill Laboratories in Berkeley to test medical marijuana samples from throughout the state. They told the CBS affiliate in San Francisco that 90 percent of the samples they tested had some trace of pathogen.

There are no requirements in place right now for marijuana to be lab tested in California. But that will soon change, as the state rolls out new regulations over the coming year for both medical and recreational marijuana.

UC Davis researchers told CBS they plan to publish results from their study Tuesday, and that they hope their findings will offer a word of caution — particularly for patients who already have weakened immune systems.

To read the full story, go to sanfrancisco.cbslocal.com.