Adolescent boys who regularly use marijuana are at increased risk of experiencing persistent, subclinical psychotic symptoms, particularly paranoia and hallucinations, even after they stop using the drug, a new study suggests.
"Perhaps the most concerning finding is that the effect of prior weekly marijuana use persists even after adolescents have stopped using for 1 year," lead investigator Jordan Bechtold, PhD, Department of Psychiatry, University of Pittsburgh Medical Center in Pennsylvania, and colleagues note.
"Given the recent proliferation of marijuana legalization across the country, it will be important to enact preventive policies and programs to keep adolescents from engaging in regular marijuana use, as chronic use seems to increase their risk of developing persistent subclinical psychotic symptoms," they add.
The study is published in the August issue of the American Journal of Psychiatry.
Participants included 1009 boys recruited from Pittsburgh public schools when they were in the first and seventh grades. Self-reported frequency of marijuana use, subclinical psychotic symptoms, and other relevant data were collected annually from age 13 to 18 years.
The researchers found that for each year the teens engaged in weekly marijuana use, their level of subsequent subclinical psychotic symptoms rose by 21%. The increase was greatest for paranoia (133%) and hallucinations (92%).
The effect of prior regular marijuana use on subsequent subclinical psychotic symptoms persisted even after the teens stopped using marijuana for a year.
"For every additional year adolescents engage in regular marijuana use, their risk of exhibiting subclinical paranoia and hallucinations in future years increases in a linear manner, and the effect of cumulative use remains significant even during periods of abstinence lasting a year," the investigators note.
They add that these effects were present after controlling for "all time-stable and several time-varying confounds" and that they found no support for reverse causation. Nor was there any evidence to support the self-medication theory ― adolescents were not more likely to use marijuana regularly following an increase in their psychotic symptoms.
Limitations of the study include the fact that it was based on a longitudinal sample of urban boys who were followed from age 13 to 18 years in one geographical area. Whether the findings hold for adolescent girls remains to be determined, the researchers note.
They also note that although evidence suggests that adolescents who report experiencing subclinical symptoms are at heightened risk of developing psychotic disorders later in life, for many young people, these symptoms are transient.
"Consistent with this notion, data collected on participants at follow-up assessments in adulthood indicated that only 2.3% of participants in the current study had developed a psychotic disorder by their late 20s or early 30s," they write.
This research is "very timely," Christian Thurstone, MD, Department of Psychiatry, University of Colorado Health Sciences Center, Denver, writes in an accompanying editorial.
"This and other studies show a preponderance of evidence linking adolescent marijuana exposure to subsequent psychosis, and the findings have important research and clinical implications."
"The key point of this article," Dr Thurstone told Medscape Medical News, "is that for certain vulnerable populations, such as adolescents, marijuana may not be 'just pot.'
"If this is the case, clinicians should screen for, treat, and refer patients with problematic marijuana use. At the same time, policy makers should take steps to increase access to effective treatments and prevent youth marijuana use in the first place."
The study had no commercial funding. The authors and Dr Thurstone have disclosed no relevant financial relationships.
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Cite this: Marijuana Tied to Persistent Subclinical Psychotic Symptoms in Teens - Medscape - Aug 15, 2016.