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,” said 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 added.

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% to 12%, Dr. Lapham said. 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 said. 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 said. 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.