Cannabis Use Disorder and Schizophrenia: Why Young Males Face the Highest Risk

Redacción HC
11/02/2024

As cannabis legalization spreads and usage becomes more normalized, public health experts are increasingly concerned about a lesser-known but serious consequence: a significantly elevated risk of schizophrenia linked to cannabis use disorder (CUD)—especially among young men.

A large-scale cohort study published in Psychological Medicine in November 2023 offers the most detailed evidence to date. Conducted by researchers from the University of Copenhagen and the U.S. National Institute on Drug Abuse (NIDA), the study tracked nearly 7 million individuals in Denmark across five decades. Their conclusion: CUD is a strong and growing contributor to schizophrenia, with the association far more pronounced in males under 30.

A Long-Term Study with Alarming Implications

This nationwide cohort study included all Danish residents aged 16 to 49 between 1972 and 2021. Over 45,000 new cases of schizophrenia were identified, with researchers analyzing links to prior diagnoses of CUD using medical registry data.

They found that the risk of schizophrenia was more than twice as high among individuals with CUD. However, when broken down by sex and age, the data revealed something more alarming:

Young males aged 16–20 with CUD were nearly four times more likely to develop schizophrenia compared to their peers without CUD.

In contrast, the same age group among females showed a less than twofold increase in risk.

Understanding the Numbers: Risk Ratios and Population Burden

Adjusted Hazard Ratios (aHR):

• Males: 2.42 (95% CI: 2.33–2.52)
• Females: 2.02 (95% CI: 1.89–2.17)

Adolescent Incidence Rate Ratios (IRR):

• Males (16–20): 3.84
• Females (16–20): 1.81

Population-Attributable Risk Fraction (PARF):

This measure estimates how many schizophrenia cases could be prevented if CUD were eliminated.

• In 2021:
  • 15% of schizophrenia cases in males were attributable to CUD
  • ~4% in females
  • In men aged 21–30, this figure jumped to 30%

In plain terms, nearly one in three schizophrenia cases among young men could be prevented by avoiding cannabis addiction.

Why the Risk Is Higher in Young Men

The researchers suggest that male adolescents and young adults may have greater neurodevelopmental vulnerability during critical periods of brain maturation. The adolescent male brain, still forming in areas related to judgment, emotion regulation, and cognitive flexibility, may be particularly sensitive to THC, the psychoactive compound in cannabis.

These findings are consistent with emerging neurobiological theories that link cannabis exposure during brain development with structural and functional changes—especially in males.

Why This Study Stands Out

While past research had established links between cannabis and psychosis, this study is the first to quantify the population-level burden across decades, providing evidence robust enough to influence policy.

Compared to earlier observational studies, this cohort analysis stands out for its:

• Extensive timespan (1972–2021)
• Massive sample size (over 6.9 million people)
• Sophisticated statistical modeling (accounting for confounders like trauma and socioeconomic status)

Despite its strengths, the study acknowledges limitations such as underreporting of mild CUD and its inability to confirm causality due to the observational design.

Public Health Implications: What Needs to Change

The study’s conclusions carry urgent messages for public health authorities, policymakers, educators, and clinicians—particularly as cannabis legalization expands worldwide.

1. Targeted Prevention Campaigns

Health campaigns should specifically target young males, raising awareness about the mental health risks of chronic cannabis use. As the study authors emphasize, early intervention may prevent thousands of schizophrenia cases.

2. Early Screening and Treatment

Health services should integrate routine CUD screening for adolescents and young adults, particularly those showing early signs of psychosis or behavioral decline. CUD treatment must be gender-sensitive and developmentally informed.

3. Cannabis Regulation and Risk Warnings

Regulatory frameworks in legalized markets must require clear health warnings—similar to those found on tobacco products—about the elevated risks of psychosis, particularly for young men. Age restrictions and public education must also be prioritized.

4. Epidemiological Monitoring

Governments should invest in ongoing surveillance of cannabis use and mental health trends to track the real-world impacts of legalization and adjust policies accordingly.

Relevance for Latin America and Global South

While the study is based in Denmark, its implications reach far beyond. In Latin America, where cannabis decriminalization is gaining momentum, similar epidemiological patterns may emerge—particularly in countries like Uruguay, Chile, and Mexico.

The findings highlight the importance of gender-aware public health campaigns, educational programs in high schools, and regional research partnerships to assess and mitigate risks.

Conclusion: A Silent Mental Health Crisis We Can Prevent

The association between cannabis use disorder and schizophrenia is real, significant, and—most importantly—preventable. By acting on evidence like this, societies can save lives, reduce suffering, and lessen the public health burden of serious mental illness.

“Young men are the most vulnerable. The cost of inaction is too high.”

Whether in Denmark or across the globe, the message is clear: Cannabis regulation must go hand in hand with science-based mental health strategies.

Topics of interest

Health Education