Will Marijuana Hurt Our Mental Health?

Will Marijuana Hurt Our Mental Health?

The legalization of marijuana continues to be a hotly debated topic in the United States. At this point in time, 23 states along with the District of Columbia have legalized marijuana for either medicinal or recreational use (or both). The impact, both good and bad, of legalization in the pioneer states is being scrutinized and studied by other states and the national government in order to guide their decision-making regarding this issue.

Cannabis has long been the most widely used illicit drug in the world and has often held a tag of being “less dangerous” than other abused substances. Some fear that the widespread legalization of the drug may further perpetuate this notion and potentially lead to even greater use of the drug among adolescent populations. This isn’t to say that there isn’t some evidence to support the use of marijuana for specific medical indications (ie, chronic pain) and let’s not also discount the negative health consequences of other legalized substances (think alcohol). However, with the increasing legality and availability of marijuana, it is important that research continues to be done on both the harmful and beneficial effects of its use so as to inform medicinal applications and legalization.

To this end, there is a significant amount of evidence to suggest that long-term cannabis use may cause long lasting neuropsychological impairment. Until recently, however, this data has largely come from small case-control studies where it is more difficult to draw the conclusion that cognitive impairment was directly related to cannabis use. More recently, data has been pulled from the Dunedin Study in New Zealand which has followed 1,037 individuals from birth to the age of 38 y/o. As part of this study, participants have been assessed regularly throughout their life about a multitude of topics and areas of interest.

In this study, cannabis use was assessed in interviews at ages 18, 21, 26, 32, and 38 y/o. Furthermore, full neuropsychological testing was conducted at age 13 y/o (before cannabis use was initiated) and again at age 38 y/o. These test results showed that persistent cannabis use was associated with neuropsychological decline across numerous domains of functioning even after controlling for other potential causative factors. Perhaps even more concerning was the fact that individuals involved in the study subjects’ lives reported noticing more cognitive problems suffered by those using cannabis regularly. Thus, it was clear that the deficits found on testing correlated to negative impacts on everyday life. The cognitive impairment was noted to be the most significant among adolescent-onset cannabis users with more persistent use being associated with a more drastic decline.

A very worrisome result of the study was that quitting cannabis use did not fully restore neuropsychological functioning among those that started using cannabis in adolescence. Thus, it seems clear and imperative that an increasing amount of effort continued to be directed towards education and prevention of cannabis initiation in adolescents. With increasing legalization, it remains to be seen whether this will become more and more of an uphill battle.

Dr. Matt Bader
Psychiatrist, Specializing in Addiction

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