One in four patients used cannabis, according to a new study, but most didn’t get their information from doctors, raising concerns.

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One in four Seattle Cancer Care Alliance patients say they have used cannabis to relieve symptoms and most were encouraged to do so by legalization, according to a new study published in the journal of the American Cancer Society.

But the vast majority of patients surveyed in the study said they wanted information from their cancer physician or nurse about cannabis use, but did not get it from them. Instead they relied on friends, family members, newspaper and magazine articles, websites or other patients.

Given the considerable use, desire for more information and likelihood legalization will spread, the study’s lead author said more research is needed on the benefits and risks of cannabis use by cancer patients. And more patients should be talking to providers about cannabis, said Dr. Steven Pergam of the Fred Hutchinson Cancer Research Center.

“I don’t want patients to hide this. I want open discussion because if we don’t know they’re using, we don’t know the best way to advise them,” Pergam said. “Ultimately what we want is a shared decision-making process.”

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Pergam said he is agnostic about cancer patients using cannabis, pending more data. But as an infectious-disease specialist, he is concerned about the risk of infection for patients with compromised immune systems.

Someone who had a bone-marrow transplant or is planning one, he said, would be at high risk for infection from fungal pneumonia, which could come from mold spores in cannabis.

Here’s how the study unfolded: In 2015 and 2016, 926 patients arriving at the Seattle Cancer Care Alliance anonymously filled out surveys about cannabis.

Most of the patients (52 percent) were male, had a college degree (59 percent) and lived within 25 miles of Seattle (52 percent). Their median age was 58.

Nearly a quarter (24 percent) considered themselves active users, with most consuming cannabis daily. Smoked plant matter and edibles were the main forms of ingestion.

Pain, nausea and stress were the most commonly cited reasons for consuming.

Research on cannabis therapy is limited, the study said. THC, the chief psychoactive ingredient in cannabis, may help relieve pain and spasticity, according to research, but data evaluating other therapeutic benefits are insufficient.

Small studies have raised concerns about the safety of cannabis in patients with compromised immune systems, the study noted.

The National Academies of Sciences, Engineering and Medicine reported earlier this year that substantial evidence indicates cannabis is effective for treating chronic pain and nausea induced by chemotherapy.

Further complicating the science is that most studies have used synthetic versions of THC created in labs, not THC derived from plants. Many medical-marijuana advocates believe in the “entourage effect,” or that the variety of chemicals in the whole plant provide more benefits than those conferred by THC alone.

Pergam and his co-authors note that studies using synthetic THC “cannot evaluate other substances, such as terpenes and flavonoids, that may enhance or provide additional therapeutic properties.”

Pergam and his co-authors acknowledged that only one in three eligible patients responded to the survey, which could have led to overrepresenting or underrepresenting cannabis use among patients.

They also said their data may not reflect use among patients in other states with laws different from those in Washington, where voters legalized pot in 2012.

Correction: A previous version of this story incorrectly spelled the name of Dr. Steven Pergam.