Does Marijuana Cause Mental Illness? What We Know About the Long-Term Effects of Weed

There are still pressing questions lingering in the hazy aftermath of marijuana's legalization in some states. As current states are observing explosions in tax revenue from their cannabis industries, and even more local governments are working quickly to make weed legal for both medical and recreational purposes, some are questioning whether the green leaf has any negative long-term health effects, like mental illness. 

The answer isn't as simple as lighting up in a state like Washington or Colorado. Though multiple studies have linked smoking marijuana to mental illnesses such as psychosis (schizophrenia) and depression, the cause and effect relation between pot and these health concerns is quite complex. 

Read more: Here Are the States That Will Possibly Legalize Marijuana in 2016

The National Institute on Drug Abuse reported on a number of studies in 2015 that found links to long-term mental health issues and smoking marijuana. The only problem, however, is there are plethora of other factors that go into a person developing mental health issues — one of those being the age of the first-time weed user. Other factors might include how frequently they use and their genetic disposition to developing such symptoms in the first place, even if they never picked up a joint.

"Recent research has found that marijuana users who carry a specific variant of the AKT1 gene, which codes for an enzyme that affects dopamine signaling in the striatum, are at increased risk of developing psychosis," the National Institute on Drug Abuse noted in 2015. "The striatum is an area of the brain that becomes activated and flooded with dopamine when certain stimuli are present. One study found that the risk for those with this variant was seven times higher for daily marijuana users compared with infrequent- or non-users."

So which came first, the chicken or the egg? While it might seem clear smoking weed can lead to psychosis after years of consumption given the user carries that gene variant, what isn't exactly obvious is whether lighting up causes mental health issues, or vice versa. As research at the state and federal level is inadequate, it makes it difficult to determine exactly what the drug's relationship might be to schizophrenia — it could be just as likely a person in the early stages of a mental health illness is more inclined to try getting high than those who aren't.

"There are several ways to explain the link between cannabis use and psychosis, and a causal relationship has not yet been firmly established," Joseph M. Pierre, co-chief of the Schizophrenia Treatment Unit at the Veterans Administration West Los Angeles Healthcare Center, wrote in a 2011 Current Psychiatry report, according to American News X.

"Current evidence supports that cannabis is a 'component cause' of chronic psychosis, meaning although neither necessary nor sufficient, cannabis use at a young age increases the likelihood of developing schizophrenia or other psychotic disorders. The overall magnitude of risk appears to be modest, and cannabis use is only one of myriad factors that increase the risk of psychosis. Furthermore, most cannabis users do not develop psychosis. However, the risk associated with cannabis occurs during a vulnerable time of development and is modifiable."

Whether or not marijuana causes mental health issues at any rate is still entirely unknown, as the most recent research suggesting there may be some sort of link. However, as more states legalize cannabis, the weed industry will quickly widen, allowing for publicly funded organizations to begin researching marijuana's long-term effects.

Until then, it might be best to remember: you can almost always have too much of a good thing — even pot.