Previous studies have linked cannabis use to increased risk of depression, anxiety, bipolar disorder, substance use disorders and psychosis, but others have not been able to replicate such findings. Now, in what is presumed to be the first national study to prospectively examine the link between cannabis use and prevalence of other mood, anxiety and substance use disorders, researchers find no link between marijuana use and mood or anxiety disorders.

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The large study, utilizing a nationally representative sample, finds no association between marijuana use and increased risk of developing mood or anxiety disorders.

Led by Dr. Mark Olfson, of the Columbia University Medical Center and New York State Psychiatric Institute, the study is published in JAMA Psychiatry.

He and his team say discrepancies between previous studies may be explained by varying age ranges, geographic locations, males vs. females or the number and type of mental disorders assessed.

More and more, states in the US are legalizing marijuana for both medical and recreational use, which has prompted further study into the benefits or risks associated with the drug.

On the positive side, one study recently suggested cannabidiol (CBD) – a compound in cannabis – could reduce seizures. And another study published last year showed that CBD can help bones to heal.

Other studies, however, are not as optimistic about the effects of marijuana. One study suggested teens who use cannabis are at risk of schizophrenia, while another claimed that a high-potency form of marijuana damages a key brain structure.

To further examine how marijuana use could affect risk of mental health and substance use disorders in the general population, the researchers from this latest study used a nationally representative sample of adults in the US.

In total, 34,653 adults were interviewed in a 3-year interval as part of the National Epidemiologic Survey on Alcohol and Related Conditions.

Results showed that, at 3 years follow-up, marijuana use was linked with increased risk of alcohol and drug use disorders, as well as nicotine dependence. There was no link between marijuana use and increased risk for mood or anxiety disorders, however.

The researchers caution that although their study does not demonstrate a causal link between marijuana use and new mental disorders, “these adverse psychiatric outcomes should be taken under careful consideration.”

They add:

From a perspective of prevention, the lack of association between more frequent cannabis use with increased risk of most mood and anxiety disorders does not diminish the important public health significance of the association between cannabis use and increased prevalence and incidence of drug and alcohol use disorders (including nicotine dependence).”

Furthermore, they point out that smoking and alcohol consumption are the first and third leading causes of preventable death, respectively, which is why they urge caution in light of their findings.

Although the strength of the study lies in its large, nationally representative sample, the authors point to some limitations.

Firstly, due to the possibility of residual confounding, the study cannot make a causal link between cannabis use and new onset of disorders. Also, because the follow-up period was only 3 years, a longer follow-up period could have revealed different prevalence patterns.

Cannabis use was self-reported in the study, not confirmed by objective means, so this presents another limitation. Furthermore, although they included the most common mental disorders, the researchers did not assess some disorders.

Still, their findings are significant, and the researchers say “physicians and policy makers should take these associations of cannabis use under careful consideration.”

Medical News Today recently reported that although marijuana use is on the rise among young adults, the rate of increase is much lower than the “doubling” previously reported.