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Adolescent cannabis use linked to subsequent hypomania

The use of cannabis in adolescence appears to be independently associated with future hypomania, and the nature of these correlations indicates a causal relationship, according to recent findings.

In the prospective study, researchers utilized data on 3,370 participants in the Avon Longitudinal Study of Parents and Children (ALSPAC), a birth cohort in the U.K. that assesses the causes of child development, health and disease. ALSPAC assessed pregnant women in Avon with due dates between April 1, 1991, and Dec. 31, 1992. Children resulting from these pregnancies were enrolled in the study.

Parents completed postal questionnaires about the health and development of study children beginning in the first trimester of pregnancy. In addition, children were seen for annual assessment, which included face-to-face interviews, psychological tests and physical examinations.

When the study children were 22 to 23 years old, they were asked to complete a thorough postal questionnaire, including a Hypomania Checklist Questionnaire. At age 17, participants were asked about their use of cannabis. These questions addressed whether they had ever used cannabis and the regularity of use within the previous year (monthly or less, two to four times a month, two to three times per week, or more than four times per week). Two cannabis use variables were constructed, with one representing the use of cannabis at any time, and the second to classify frequent cannabis use vs. infrequent or no cannabis use.

The researchers collected information about various potential risk factors and confounders. These included gender, early environmental risk factors, alcohol/drug abuse, physical/sexual abuse, and other adversity circumstances as measured by the Family Adversity Index (FAI). Participants were assessed at age 18 for psychotic symptoms, measured by the Psychosis Like Symptom Interview. Depression symptoms were also evaluated at age 17 to 18 years using the validated Revised Clinical Interview Schedule (CIS-R).

Using regression analysis, the researchers evaluated the prospective association between the use of cannabis at age 17 and subsequent hypomania at age 22 to 23 years. This analysis was adjusted for gender, early environmental risk factors, alcohol and drug use, and depression and psychotic symptoms.

The researchers found that in unadjusted analysis, hypomania at 22 to 23 years was significantly associated with both any cannabis use and cannabis use at least two to three times weekly. A dose-response relationship was also seen, with a stronger correlation for use at least two to three times weekly. These correlations were only slightly diminished after adjustment for psychotic and depression symptoms. The associations were further weakened after adjustment for other drug and alcohol use, but remained strong. Finally, adjustment for gender, family adversity, and childhood abuse attenuated the associations further, but the associations retained their significance (OR = 2.21; 95% CI, 1.49-3.28).

The use of cannabis at least two to three times per week was also a significant predictor of both depression (OR = 2.48; 95% CI, 1.6-3.83) and psychotic symptoms (OR = 3.33; 95% CI, 2,01-5.53).

Although the correlation between cannabis use and hypomania was not significantly mediated by depression or psychotic symptoms, the use of cannabis significantly mediated correlations of gender and abuse with future hypomania.

“We show adolescent cannabis use is an independent risk factor for future hypomania, and the nature of the associations found is suggestive of a causal link, though the gold standard for inferring causality of course remains intervention,” the researchers wrote. “The study also identifies cannabis use as a candidate mechanism for explaining how childhood abuse may lead to hypomania in adulthood.” – by Jennifer Byrne

Disclosure: The authors report no relevant financial disclosures.