Drivers with alcohol interlock devices increased cannabis use, and it persisted after device removal | Research

The takeaway

Drivers who cut alcohol use while an interlock device was installed significantly increased cannabis use, and that increase continued even after the device was removed.

Policymakers, traffic safety researchers, and clinicians working with DUI offenders.

Cannabis use continued rising even after the interlock device was removed

What the researchers found

Among 189 DUI-convicted drivers, those who decreased alcohol use while an ignition interlock device was installed significantly increased cannabis use, which continued to rise after the device was removed.

Why it matters

Alcohol interlock devices effectively prevent drunk driving, but this study reveals an unintended consequence: some drivers substitute cannabis for alcohol, creating a different impairment risk.

The numbers in context

189 participants completed all three waves. Cannabis use increased across the study period overall. Drivers who decreased alcohol during IID use significantly increased cannabis, with further increases after device removal.

How the study worked

Three-wave longitudinal study of 189 New York State DUI-convicted drivers from 2015 to 2020. Oral fluid and blood samples measured cannabis use; hair samples measured alcohol use. Assessed at IID installation, removal, and 6-month follow-up.

What this study cannot tell us

Sample size was moderate at 189. The study was conducted in New York State, which may limit generalizability. Self-selection effects may be at play, as those who reduce alcohol may already be predisposed to use other substances.

How to read the evidence

Moderate: three-wave longitudinal design with biological measures, but moderate sample size and observational design.

When this study was published

Published in 2022.

The bigger picture

This finding highlights the concept of substance substitution in impaired driving interventions. Preventing one type of impaired driving may inadvertently increase another.

Questions still open

Would adding cannabis monitoring to IID programs reduce this substitution effect? Do drivers who increase cannabis use also drive while impaired by cannabis? Could counseling during IID installation prevent substance switching?

Common questions

What is an alcohol ignition interlock device?

It prevents a car from starting if the driver's breath alcohol exceeds 0.025%. It is commonly mandated for DUI-convicted drivers.

Did all drivers increase cannabis use?

No. The significant increase was specifically among drivers who decreased their alcohol use while the device was installed, suggesting a substitution pattern rather than a universal effect.

What are the policy implications?

The researchers recommend supplemental treatment interventions during IID installation to address the potential for substance switching and polysubstance use.

Read the original research

Cannabis Adaptation During and After Alcohol Ignition Interlock Device Installation: A Longitudinal Study.

Journal of studies on alcohol and drugs, 83(4), 486-493

View on PubMed ↗

Citation

Scherer, Michael; Romano, Eduardo; King, Sagan; Marques, Paul; Romosz, Ann; Taylor, Eileen; Nochajski, Thomas H; Voas, Robert; Manning, Amy; Tippetts, Scott. (2022). Cannabis Adaptation During and After Alcohol Ignition Interlock Device Installation: A Longitudinal Study.. Journal of studies on alcohol and drugs, 83(4), 486-493.