In two experiments totaling 1,601 young adults, receiving hypothetical genetic test results showing heightened schizophrenia risk from marijuana increased intentions to avoid cannabis, especially among prior users.
Genetic counselors, public health prevention designers, and researchers studying personalized medicine for substance use.
Genetic predisposition information increased marijuana avoidance, especially in prior users
What the researchers found
Participants told they had a genetic predisposition for marijuana to increase schizophrenia risk rated the likelihood and importance of avoiding marijuana as significantly higher than controls. In the nationally representative sample, this effect was strongest among those who had previously used marijuana. Conversely, being told one lacked such a predisposition tended to lower avoidance intentions, raising concerns about a "genetic license" effect.
Why it matters
As genetic testing becomes more common, understanding how personalized risk information affects substance use behavior is critical. This study suggests genetic cannabis-psychosis risk information could be a powerful prevention tool, but the "no predisposition" condition raises ethical concerns.
The numbers in context
Experiment 1: 801 participants (Mechanical Turk). Experiment 2: 800 participants (nationally representative, ages 18-30). Predisposition condition: increased avoidance intentions. No-predisposition condition: decreased avoidance in Experiment 1. Prior marijuana use moderated effects in Experiment 2.
How the study worked
Two randomized experiments. Experiment 1: 801 US young adults from Mechanical Turk. Experiment 2: 800 nationally representative US adults aged 18-30. Participants randomized to three conditions: genetic predisposition present, absent, or no genetic testing (control). Measured intentions to avoid marijuana.
What this study cannot tell us
Hypothetical scenarios, not actual genetic tests. Self-reported intentions may not predict behavior. Mechanical Turk sample in Experiment 1 may not be representative. Short-term measurement only.
How to read the evidence
Two randomized experiments with adequate samples, one nationally representative. Limited by hypothetical scenarios and self-reported intentions.
When this study was published
2021 experimental study.
The bigger picture
The finding that prior marijuana users were most responsive to genetic risk information is encouraging for targeted prevention. However, the risk that genetic "all-clear" results could reduce caution (the genetic license effect) needs careful consideration before implementing such testing.
Questions still open
- Would real genetic test results produce similar behavioral changes? How should genetic cannabis risk information be communicated to minimize the "license" effect? Would personalized genetic counseling be effective for cannabis prevention?
Common questions
Could genetic testing prevent marijuana use?
Is there a downside to genetic testing for cannabis risk?
Read the original research
Experimentally exploring the potential behavioral effects of personalized genetic information about marijuana and schizophrenia risk.
Journal of psychiatric research, 140, 316-322
Citation
Lebowitz, Matthew S; Appelbaum, Paul S; Dixon, Lisa B; Girgis, Ragy R; Wall, Melanie M. (2021). Experimentally exploring the potential behavioral effects of personalized genetic information about marijuana and schizophrenia risk.. Journal of psychiatric research, 140, 316-322. https://doi.org/10.1016/j.jpsychires.2021.05.066
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