The questions about marijuana law enforcement and our legal system as well as the quagmire of politics and de facto encouragement of recreational marijuana use has dwarfed the science regarding the risk-benefit or harmful effects of this drug in the U.S. Advocates for the legalization, sale and recreational use of crude cannabis assert that it is a relatively harmless “natural herb” with numerous medicinal properties. However, unlike the somewhat notorious club drug ketamine, which is in controlled trials for depression, cannabis trials are more anecdotes than evidence-based controlled research.

One of the biggest concerns germane to the question of harm has to do with “age of use” risks related to numerous reports of psychiatric problems and outright mental illness associated with both acute intoxication and chronic use of marijuana that began during childhood or adolescence.

What We Know

The best available evidence has demonstrated a causal relationship between smoking marijuana and the subsequent use of other drugs including alcohol. DuPont and others have also described the ascendance to the use of other so called “harder drugs,” e.g., the “Gateway Drug” theory. These associations are difficult to understand because while it is true that most heroin users have used marijuana, most marijuana users have not progressed to heroin.

While tobacco first was the rule for decades, it is now widely understood and established that marijuana is usually the first drug used by a young person who then goes on to try other drugs. I have never liked the term gateway drug because it intimates that marijuana is “lesser than” a harmful or “hard” drug. In my work, smoking is the gateway event allowing the smoker to inject the drug without a needle.

Marijuana is not like cocaine or opioids. After alcohol, it’s the most cited reason for entering drug treatment in the U.S. And why do people enter treatment? Loss of control, school failures, social failure and repeated harmful consequences.

Second, marijuana is in a class all by itself. Most marijuana addicts who seek treatment become impaired to the point that they cannot manage their lives. Additionally, research funded by the National Institute of Drug Abuse (NIDA) utilizing sophisticated brain imaging techniques has shown neuroadaptive changes in the brain of adolescents who smoke marijuana. Director of NIDA, Dr. Nora Volkow, reports:

Studies have shown that exposure to cannabinoids during adolescent development can cause long-lasting changes in the brain’s reward system as well as the hippocampus, a brain area critical for learning and memory.

“Neuroadaptation” is the polite way scientists say brain damage. For example, a recent report in the journal Brain reveals neural-connectivity impairment in several brain regions following prolonged cannabis use that was initiated during adolescence or young adulthood.

In an excellent review by Hanna & Perez (2017), the authors performed a meta-analysis, demonstrating a correlation between marijuana use and mental illness. In nearly every review, younger users of cannabis were more likely to develop psychiatric disorders. The association was strongest between cannabis use among children and adolescents and psychosis. The evidence regarding the association between major depression, bi-polar depression and anxiety disorder were widely reported; however, the quality of this evidence was often subject to confounding variables, including early life trauma, withdrawal syndrome, design flaws and uncertainty regarding periods of abstinence. However, the authors state:

Age at the time of cannabis use appears to be an important factor with stronger associations observed between adolescent onset cannabis use and later onset of psychiatric disorders.

Moreover, the concordance rate between SUDs and depression is 45-65%. Given that cannabis use disorder, as previously stated, is the second leading reason cited for all admissions to SUD treatment, it follows that a statistically significant association between cannabis use and depression exists.

Certainly, more research is needed to elucidate the neural effects of this poorly understood drug on the health and welfare of those who use it regularly, especially children and teens.