Marijuana Use in Early Adolescence Triples Risk of Psychosis At Age 18
Hannah J. Jones and colleagues reported in the journal JAMA Psychiatry in 2018 that early- and late-onset marijuana use increased the risk of psychosis at age 18 (odds ratio 3.7 to 2.97). Interestingly, early-onset cigarette use also increased risk of psychosis, but much of the link between cigarette use and psychosis disappeared after correcting for confounding variables.
The data on 5,300 participants born from 1991 to 1992 came from the Avon Longitudinal Study of Parents and Children. Researchers followed up with the participants about their use of marijuana and cigarettes at least three times between the ages of 14 and 19.
Editor’s Note: These data add to a host of epidemiological data that smoking marijuana doubles the risk of psychosis. Risk is further increased among people with a common genetic variant (val/val) of the gene for COMT (catechol-O-methyltransferase), which metabolizes prefrontal dopamine. The variant, which includes two valine amino acids, functions better than other variants that include methionine amino acids. People with val/met or met/met COMT genes metabolize dopamine more slowly, making them relatively protected.
The data are also pretty strong that early heavy use of marijuana is a risk factor for new onset of both bipolar disorder and schizophrenia (and not just an earlier onset in those who might have been vulnerable otherwise).
While marijuana use has become more mainstream with its legalization in many states, its recreational use still carries risks of mental illness. In addition to increasing psychosis risk, marijuana use can also make bipolar disorder more difficult to treat.
A minor component of marijuana, cannabidiol, can have some positive effects, but what you get most of when consuming marijuana is tetrahydrocannabinol (THC), which produces symptoms that resemble psychosis.
Data in rats indicate that a father rat’s use of THC as an adult increases the risk that his offspring (with which he has no contact) will be prone to opiate addiction. The effect is an epigenetic one, conveyed by chemical changes in the father’s DNA that get passed on to the next generation via changes that persist in his sperm. We don’t know if this also happens with humans. So even if you are not worried about your own health, avoiding marijuana use might be good for your children.
Cannabis Use May Cause Schizophrenia
Cannabis use has been linked to schizophrenia risk, and new genetic research suggests a causal relationship between the two. In a 2017 article in the journal Molecular Psychiatry, researcher Julian Vaucher and colleagues reported that lifetime cannabis use was linked to schizophrenia even when the researchers controlled for 10 genotypes weakly associated with lifetime cannabis use. This makes it unlikely that the schizophrenia caused the cannabis use, suggesting instead that it is the cannabis use that leads to a schizophrenia diagnosis.
Vaucher and colleageus also controlled for genetic associations between cigarette smoking and cannabis use to eliminate cigarette use as a third variable causing the association between cannabis and schizophrenia.
The study by Vaucher and colleagues included 34,241 people with schizophrenia and 45,604 healthy controls.