How should we talk about marijuana with our patients? For psychiatrists, the topic usually arises with respect to two key areas:

1. the potential adverse effects of marijuana use, especially upon those with other psychiatric disorders and our youth, and


2. the question of the legitimate medical benefit of medical marijuana for particular medical and psychiatric conditions (Hill KP, J Psychiatric Practice 2014;20(5):389–391).

In both of these areas, it might seem easy to deliver a harsh anti-marijuana message, emphasizing the harms of marijuana use and the notion that medical marijuana is not supported by scientific evidence. However, an evidence-based perspective is closer to a middle ground than either of the extreme views, and being a “moderate” on these issues will give you greater credibility in the eyes of patients.

Adverse Effects
Acute effects of getting high
The adverse effects of marijuana use are well-documented (Volkow ND et al, N Engl J Med 2014;370(23):2219–2227). The immediate effects of getting high are not particularly controversial. They include impaired judgment and short-term memory, as well as impaired driving. Patients often ask about the difference between alcohol and marijuana’s effects on driving. The evidence shows that both marijuana and alcohol can impair driving, but in different ways. Drunk driving is associated with careless mistakes, or “errors of omission”—driving too fast while not checking your mirrors, for example, where driving under the influence of marijuana may lead to “errors of commission”—being overly cautious but driving 30 miles per hour in a 55 miles-per-hour zone, for example (Sewell RA et al. Am J Addict 2009;18(3):185-193).

The bottom line is that getting high causes acute cognitive impairment and is not compatible with doing well at many of life’s important tasks, such as work, studying, and driving. Given that many psychiatric patients are already struggling with such tasks, it is useful to consider the degree to which marijuana may be hampering these tasks—this is one way to use motivational interviewing techniques to broach the topic of reducing or stopping recreational marijuana use.

Chronic effects: Low IQ and psychosis
What about the effects of long-term, chronic use of marijuana? My biggest concern is that chronic use can affect young people, whose brains are still developing. The most publicized study about long-term effects was the Meier et al (2012) study. This study reported that early (teen) and regular use of marijuana is associated with up to an 8-point decline in IQ (Meier MH et al, Proc Natl Acad Sci USA 2012;109(40):642–649). Subsequently, a paper was published in the same journal that questioned the causal inferences made by Meier’s group, so more research is needed (Rogerberg O, Proc Natl Acad Sci USA 2013;110(11):4251–4254). (Editor’s Note: For further reading, see this Washington Post article.)

My take on the studies thus far is that long-term regular use is almost certainly a cause of long-term decrease in intelligence. I tell my younger patients that if they are smoking daily they are likely to be permanently sabotaging themselves. There are better ways to deal with life’s stresses, and both therapy and medications can help without causing what is essentially brain damage.

Another potential effect of early and regular marijuana use is increased likelihood for developing psychosis. For example, DiForti et al (2015) showed that young regular users of high-THC marijuana in the UK (average THC content in the United States) were five times more likely than others to develop a psychotic disorder (Di Forti M et al, The Lancet Psychiatry 2015;2:233–238). While such retrospective studies do not imply causality, the evidence is concerning and is another reason to steer psychiatric patients away from frequent pot use.

Does marijuana use interfere with psychiatric treatment?
We are reasonably concerned that marijuana use will adversely affect how our patients respond to medications or psychotherapy aimed at treatment of other psychiatric disorders. It’s quite clear that the drug can worsen depression and anxiety (Crippa JA et al, Hum Psychopharmacol 2009; 24(7):515–523, and Degenhardt L et al, Addiction 2003;98(11):1493–1504). The effect on anxiety is especially difficult for patients to grasp because marijuana users often feel less anxious immediately after using. When the effects of marijuana wear off, however, there is a “rebound” phenomenon whereby the patient’s baseline level of anxiety actually increases.

What about marijuana’s effects on treatment outcome? There’s not too much research to guide us here. We published one study examining whether pot use adversely affected treatment outcome in adolescents with opioid use disorder (Hill KP et al, Drug Alcohol Depend 2013;132(1–2):342–345). In a secondary data analysis of 152 opioid-dependent youth ages 15–21 on buprenorphine, we found that both past marijuana use and current marijuana use had no effect upon opioid use in the sample. While the evidence is mixed on the issue of whether marijuana affects treatment outcome, most papers found results similar to ours. In general, I tell patients that marijuana is likely to worsen depression and anxiety, but I don’t withhold medication treatment from such patients because there just isn’t enough evidence that the drug actively interferes with such treatment.

Medical Marijuana
As the debate over the utility of marijuana for a host of medical conditions continues, patients wonder if medical marijuana might help them. Some patients may not ask about it and just announce that they have obtained a medical marijuana card and are using it for self-treatment. Here’s how I approach this difficult but increasingly common situation.

First, I make sure my patients understand the evidence for medical marijuana’s efficacy. There are only two FDA indications for cannabinoids, which are nausea and vomiting associated with chemotherapy and appetite stimulation in certain wasting illnesses like HIV. There is also strong evidence that marijuana helps chronic pain, neuropathic pain, and muscle spasticity associated with multiple sclerosis (Hill KP, JAMA 2015;313(24):2474–2483). Beyond these indications, though, the evidence is either negative or lacking.

In my experience, patients will say that medical marijuana essentially treats whatever ails them, from PTSD to anger issues to aches and pains of all varieties. I tell them that the evidence is just not there and that they may well be doing themselves more harm than good. I emphasize that even for the short list of conditions for which there is some evidence, marijuana is never considered the first-line treatment.

To sum up, while there are some legitimate medical uses for marijuana, most psychiatric patients are going to experience more harm than benefit. Take each case individually, but don’t hesitate to lay out the evidence, and to educate your patients even if they might be dismayed. In the long run, they’ll be grateful.