News Release

As access to legal marijuana increases, Kaiser Permanente researchers explore patient use

Routinely asking about cannabis use can better serve patients by helping clinicians start conversations about the risks and benefits.

Peer-Reviewed Publication

Kaiser Permanente

About 1 in 7 adult primary care patients visiting medical offices reported having used marijuana at least once in the past year, according to a study conducted by Kaiser Permanente researchers since Washington state legalized nonmedical cannabis use in 2014.

In young adults, that rate was higher: nearly 2 in 5. Young adults -- especially men age 18-29 who had depression or used tobacco -- were also much more likely than others to use cannabis every day. These findings raise concerns, according to first author Gwen T. Lapham, PhD, MPH, MSW, a Kaiser Permanente Washington Health Research Institute research associate. "Much remains to be learned about marijuana use, while legalization is spreading."

"Routinely asking about cannabis use in primary care is part of whole-person care, and it's the first step to starting a conversation between patients and their primary care providers," says the study's principal investigator, Katharine A. Bradley, MD, MPH, a senior investigator at KPWHRI and internal medicine physician with Washington Permanente Medical Group.

"Our findings highlight the need for primary care clinicians to be aware of the benefits and harms that patients may be experiencing due to their cannabis use -- and initiating a conversation is only the start in that process," Dr. Bradley adds.

These conversations can help providers assess the intensity of patients' use, perceived risks and benefits, and reasons why patients are using cannabis, for instance possibly for symptoms of a treatable condition.

Kaiser Permanente researchers in Washington analyzed information from medical visits, keeping private the information that could help identify any of the 22,000 patients in the study. Published in the Journal of the American Board of Family Medicine, "Frequency of Cannabis Use among Primary Care Patients in Washington State" is among the first U.S. studies to evaluate the population-based prevalence of patient-reported cannabis use among primary care patients, particularly in a state where nonmedical use is legal.

After alcohol and tobacco, marijuana is the most commonly used drug in the United States. In recent years, the concentration of tetrahydrocannabinol (known as THC), the main psychoactive and addictive component, has increased in cannabis plants from 3 percent to 12 percent, Dr. Lapham says. And new products -- like concentrated hash oil and synthetic cannabinoids -- are raising the potency and risk for addiction.

"Some groups of patients are more likely to use cannabis daily and be at higher risk for complications such as cannabis use disorder -- as well as some harms that are not yet completely understood," Dr. Lapham says. Among patients who reported using cannabis, about half used it at least monthly -- and about 1 in 5 used it daily, the researchers found. From a quarter to half of people who use daily are estimated to develop a cannabis use disorder, where patients can't cut down on their use despite accumulating use-related problems.

"Widespread daily use in young men with depression is concerning, because using cannabis can worsen depression and anxiety," Dr. Lapham says. Although counseling can improve outcomes, no medication is known to be effective or approved to treat cannabis use disorder, she added.

Medical cannabis use is now legal in 29 states, and nonmedical use is legal in eight states. In 2014, Washington state became one of the first two states to sell cannabis for nonmedical ("recreational") use. With expanding legalization of cannabis use, the number of users is projected to grow during the next decade.


The National Institute on Drug Abuse (awards UG1DA040314-01S1 and UG1 DA01581) and the Agency for Healthcare Research and Quality (award R18 HS023173) supported this research.

About Kaiser Permanente Washington Health Research Institute

Kaiser Permanente Washington Health Research Institute (KPWHRI) improves the health and health care of Kaiser Permanente members and the public. The Institute has conducted nonproprietary public-interest research on preventing, diagnosing, and treating major health problems since 1983. Government and private research grants provide our main funding. Follow KPWHRI research on Twitter, Facebook, Pinterest, LinkedIn, or YouTube. For more information, go to:

About Kaiser Permanente

Kaiser Permanente is committed to helping shape the future of health care. We are recognized as one of America's leading health care providers and not-for-profit health plans. Founded in 1945, Kaiser Permanente has a mission is to provide high-quality, affordable health care services and to improve the health of our members and the communities we serve. We currently serve 11.7 million members in eight states and the District of Columbia. Care for members and patients is focused on their total health and guided by their personal Permanente Medical Group physicians, specialists and team of caregivers. Our expert and caring medical teams are empowered and supported by industry-leading technology advances and tools for health promotion, disease prevention, state-of-the-art care delivery and world-class chronic disease management. Kaiser Permanente is dedicated to care innovations, clinical research, health education and the support of community health. For more information, go to

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