Marijuana: A Possible Treatment for Depression?

Recently there has been debate over whether the popular recreational drug marijuana (see image at left) has legitimate medical uses. Several states, including California, have decriminalized marijuana usage for patients who have been told by their doctors that they could benefit from the drug. The main, if controversial, recognized medical use of marijuana has to do with its supposed pain-relieving effect. It is often recommended to cancer and AIDS patients to alleviate the chronic pain that often accompanies those diseases. According to the National Organization for Reforming Marijuana Laws (NORML), an organization that promotes the legalization of marijuana, it has also been recognized for “symptomatic relief for a number of medical conditions, including nausea and vomiting, stimulating appetite, promoting weight gain, and diminishing intraocular pressure from glaucoma.” However, the Drug Enforcement Agency of the United States classifies marijuana as a Schedule I drug, meaning it, among other things, “has no currently accepted medical use in treatment in the United States.” Nevertheless, a new study (the full text article requires a subscription) published in the current issue of The Journal of Neuroscience may add antidepressant to marijuana’s list of medical uses.

The new research studied the effect of tetrahydrocannabinol (THC), the active chemical in marijuana, on rats. Among other experiments, the researchers used a “Forced Swim Test” or FST to evaluate the drug’s antidepressant properties. This test involves placing the rats in water too deep to stand in and seeing how long it takes until they give up trying to swim. The basic idea is that more “depressed” rats will give up on surviving sooner. In the words of the study, “The FST is both sensitive and selective for clinically effective antidepressants, has been repeatedly validated, and is currently the most popular model for detecting antidepressant activity attributable to its simplicity, reliability, and high predictive validity.” The researchers also directly measured serotonin activity in the rats’ brains. The results showed that low doses of THC produced similar effects to SSRI (selective serotonin reuptake inhibitor) antidepressants, meaning they increased the rats’ swimming behavior in the FST (see graph below right where WIN is the THC and DIM is the SSRI used for comparison) and increased serotonin activity in their brains. On the other hand, high doses of THC did not affect the results of the FST and actually lowered serotonin activity. THC exerts its effect by activating the brain’s endocannabinoid system, which can be thought of as the brain’s stress-recovery mechanism.

I should note that this study does not necessarily translate to typical recreational marijuana use in humans. First, even though rats are often used as models for human diseases, the human brain is still infinitely more complex than the rat brain and therefore THC may influence it differently. Also, recreational marijuana is usually smoked, and this makes it difficult to control the amount of THC entering the bloodstream. As stated above, high doses of THC have detrimental effects on the brain systems thought to be responsible for mood, and therefore the researchers cautioned against attempting to use smoked marijuana as an antidepressant. In addition, marijuana and particularly smoked marijuana have other negative effects including “frequent respiratory infections, impaired memory and learning, increased heart rate, anxiety, panic attacks and tolerance,” as indicated by the White House’s fact sheet on the drug. Marijuana has also been shown in some studies to be addictive and cause physical dependence.

It would be interesting to see more research done on this subject, as today’s classes of antidepressants are by no means one hundred percent effective. Unfortunately, due to marijuana’s tight scheduling in the United States, it is difficult for American researchers to conduct quality studies on its effects. Notably, the study mentioned above was done in Canada at McGill University and the University of Montreal, both in Quebec. In order for scientists to research marijuana in this country, they must obtain it from the National Institute on Drug Abuse (NIDA). Numerous scientists have criticized this supply as being less potent than the drug that is usually found on the street. Furthermore, an article in Scientific American points out that the government is reluctant to fund studies that propose to look for health benefits of marijuana. Instead federal funding is focused on studies of its detrimental effects, perhaps because the nation's drug policy is based on the assertion that marijuana has no medical use whatsoever. I think this policy is unwise because it might limit the development of potential new treatments for depression as well as other illnesses. When possible, the government should promote open scientific inquiry, not attempt to stifle it because the findings may contradict the reasoning for its policies.