Important Questions About the Impact of Medical Marijuana on People With Serious Mental Illness

Despite the lack of strong evidence for efficacy and the known risks of marijuana use, states have implemented a variety of medical marijuana programs. For example, in New Hampshire, the state legislature has identified 21 diagnoses that are eligible for treatment with medical marijuana, including moderate chronic pain and PTSD. If a licensed clinician determines that a patient has one of the 21 approved diagnoses, he or she may provide the patient with a registry identification card. People with cards may buy up to two ounces of marijuana every 10 days at an “alternative treatment center.” These for-profit businesses are licensed by the state to grow and sell marijuana products, including edibles, vaping oils, lotions, transdermal patches, and plant material for smoking. Purchases may be made online or in person from a large menu of products with appealing, nonmedical names and THC potencies that are much higher than potencies studied for medical indications such as pain. For example, products include Gorilla Glue Ethanol Shatter, with 75.8% THC potency; Billy Club Sativa, with 19.04% THC and <.05% CBD potencies; and Shark Shock Flower, with 9.21% THC and 11.88% CBD potencies (11).

Although product labeling of medical marijuana is required, recent studies suggest that regulatory infrastructures do not yet ensure product safety or consistency. For example, in various states, a third of samples were adulterated with pesticides (12), product labeling was incorrect from 60% to 80% of the time (13,14), and laboratory testing results were inconsistent (15).

In our clinical experience, many people with serious mental illness access medical marijuana for an array of indications, and many of them have experienced problems, including worsening psychosis, anxiety, cognitive impairment, and addiction. Community clinicians may not fully understand the mental health and addiction liabilities of THC, and they may not coordinate their recommendation for marijuana use with other providers. Thus the potential benefits of CBD may be overemphasized compared with the potential harm from THC. The following case exemplifies the complications that people with serious mental illness may experience when using medical marijuana.

Mr. D. is a 50-year-old man with well-controlled bipolar disorder and chronic back pain from a car accident that occurred 10 years earlier. When his pain recently worsened, his primary care provider (PCP) provided a marijuana card and guidance for use of medical marijuana for pain, which he used in the evening about three times weekly, with improvements in sleep and pain. Nine months later, however, he presented to his psychiatrist with concerns that he was “going crazy with side effects from the mood stabilizers.” He appeared confused, disorganized, and hypomanic. His psychiatrist learned that Mr. D. had increased his marijuana use to address increased pain, with his PCP’s advice, to three times daily. The psychiatrist provided education and discussed the potential risks of marijuana use with Mr. D., as she would when discussing any medicine. In this case, the destabilizing effects of THC on cognition and mood, in addition to its addiction liability, were particularly relevant. Even with this information, Mr. D. strongly wished to continue using marijuana for pain, so he and the psychiatrist agreed that he would switch to a high-CBD, low-THC product and reduce use to once in the evening. They agreed that if problems with cognition and hypomania continued, he would cut back further. The psychiatrist called the PCP to coordinate Mr. D’s care, and Mr. D.’s condition restabilized over the following weeks.

People with serious mental illness may experience many adverse effects and more easily develop an addiction with marijuana use. Further research is needed to assess the potential benefits of CBD among people with serious mental illness and to clarify whether any level of THC exposure by this group is safe. It is also important to evaluate whether use of marijuana affects use of other substances, such as opioids, among people with serious mental illness. Given the U.S. trajectory toward legalization of marijuana, clinicians need to incorporate knowledge about marijuana into their clinical work, communicate with providers who endorse marijuana and with dispensaries that provide it, and also provide guidance in order to reduce harms among people with serious mental illness who choose to use marijuana.