Link between cannabis use disorder, schizophrenia strongest in young men

Key takeaways:

• There were sex differences in the link between cannabis use disorder and schizophrenia.
• Among young people, men had a much stronger link between cannabis use disorder and schizophrenia compared with women.

The association between cannabis use disorder and schizophrenia was stronger in men compared with women, particularly among people aged 16 to 20 years, according to a study published in Psychological Medicine.

Carsten Hjorthøj, PhD, an associate professor at the Copenhagen Research Center for Mental Health, and colleagues identified people listed in linked Danish national registers who were born before Dec. 31, 2005, and who were aged 16 to 49 years at some point from 1972 to 2021. The researchers evaluated the associations between cannabis use disorder (CUD) and schizophrenia within this population.

Among 6,907,859 people included in analyses, there were 45,327 cases of schizophrenia. Compared with people who did not have CUD, those who did were at greater risk for subsequent schizophrenia diagnosis (adjusted HR = 2.31; 95% CI, 2.24-2.4).

There was a greater risk for schizophrenia diagnosis after CUD among men (aHR = 2.42; 95% CI, 2.33-2.52) compared with women (aHR = 2.02; 95% CI, 1.89-2.17). Further stratification by age revealed the adjusted incidence rate ratio (aIRR) for schizophrenia diagnosis following CUD was more than twice as high for boys and men aged 16 to 20 years (aIRR = 3.84; 95% CI, 3.43-4.29) compared with girls and women the same age (aIRR = 1.81; 95% CI, 1.53-2.15).

Across the study period, the annual percent change in the population attributable risk fraction (PARF) of CUD in the incidence of schizophrenia was higher among men (annual percent change, 4.8; 95% CI, 4.3-5.3) compared with women (annual percent change, 3.2; 95% CI, 2.5-3.8).

“These results suggest that during 1972 throughout 2021, the annual average percentage change in the PARFs of CUD on the incidence of schizophrenia was consistently higher in males than in females,” according to the study (P < .0001).

Notably, the PARF for men was 15% in 2021, compared with 4% among women, the researchers wrote.

“Increases in the legalization of cannabis over the past few decades have made it one of the most frequently used psychoactive substances in the world, while also decreasing the public’s perception of its harm,” Hjorthøj said in a press release. “This study adds to our growing understanding that cannabis use is not harmless, and that risks are not fixed at one point in time.”

References:

• Hjorthøj C, et al. Psychol Med. 2023;doi:10.1017/S0033291723000880.
• Young men at highest risk of schizophrenia linked with cannabis use disorder. https://www.nih.gov/news-events/news-releases/young-men-highest-risk-schizophrenia-linked-cannabis-use-disorder. Published May 4, 2023. Accessed May 16, 2023.