Combining Alcohol and Cannabis Sharply Increased Self-Harm Risk in Hospitalized Teens | Research

The takeaway

Among 71 adolescents hospitalized for suicide risk, neither cannabis nor alcohol alone predicted self-harm on a given day, but using both together increased the odds by over 30-fold.

Adolescent psychiatrists, suicide prevention researchers, substance use counselors

Co-occurring alcohol and cannabis use increased same-day self-harm odds by 30.5 times

What the researchers found

While neither cannabis nor alcohol use independently predicted nonsuicidal self-injury (NSSI) on a daily level, co-occurring alcohol and cannabis use on the same day increased the odds of NSSI by 30.5 times (OR=30.5, p<0.05) in the 90 days prior to hospitalization.

Why it matters

The dramatic interaction between alcohol and cannabis for self-harm risk suggests that polysubstance use, not either substance alone, may be a critical warning sign in suicidal adolescents.

The numbers in context

71 adolescents; 75% female; mean age 15.79; suicide planning OR=4.47 for NSSI; suicidal ideation OR=10.09 for NSSI; co-occurring alcohol+cannabis use OR=30.5 for NSSI (p<0.05); neither substance independently significant.

How the study worked

Mixed effect models analyzing daily trajectories of alcohol use, cannabis use, suicide planning, and NSSI over the 90 days prior to psychiatric hospitalization in 71 adolescents (75% female, mean age 15.79).

What this study cannot tell us

Small sample size (71 adolescents); all participants had used alcohol, limiting generalizability; retrospective daily recall subject to memory bias; hospitalized sample may not represent community adolescents.

How to read the evidence

Small longitudinal study with daily-level analysis of high-risk adolescents, limited by sample size and retrospective recall.

When this study was published

Study of adolescents hospitalized for suicide risk.

The bigger picture

This finding shifts the focus from individual substances to their combination as a risk factor, suggesting that screening for polysubstance use in suicidal adolescents may be more informative than asking about each substance separately.

Questions still open

What biological or psychological mechanism drives the interaction between alcohol and cannabis for self-harm? Would polysubstance screening tools in psychiatric settings improve risk assessment?

Common questions

Does cannabis use increase self-harm risk in teenagers?

In this study, cannabis use alone did not independently predict self-harm. However, when adolescents used both cannabis and alcohol on the same day, the odds of self-harm increased dramatically (over 30-fold).

Why is the combination more dangerous than either substance alone?

The study did not determine the mechanism, but the sharp increase in risk with combined use suggests that alcohol and cannabis together may lower inhibitions and intensify emotional distress in ways that neither substance does on its own.

Read the original research

The relationship between alcohol and cannabis use with nonsuicidal self-injury among adolescent inpatients: Examining the 90 days prior to psychiatric hospitalization.

Addictive behaviors, 114, 106759

View on PubMed ↗Publisher’s paper ↗

Citation

Sellers, Christina M; Díaz-Valdés, Antonia; Oliver, Michelle M; Simon, Kevin M; O'Brien, Kimberly H McManama. (2021). The relationship between alcohol and cannabis use with nonsuicidal self-injury among adolescent inpatients: Examining the 90 days prior to psychiatric hospitalization.. Addictive behaviors, 114, 106759. https://doi.org/10.1016/j.addbeh.2020.106759