Alcohol Impairs Thinking While Cannabis Mainly Shifts Mood, Study Finds | Research

The takeaway

In a controlled trial of 28 young adults, cannabis primarily affected mood and subjective experience while alcohol primarily impaired cognitive and psychomotor performance, with combined effects that were additive at most.

People interested in how cannabis and alcohol differ in their acute effects on thinking and performance

28 participants, 4 conditions

What the researchers found

Cannabis increased tension-anxiety, confusion, euphoria, and sedation ratings but had minimal impact on cognitive test scores. Alcohol impaired verbal recall, digit symbol substitution, and fine motor tasks but had minimal impact on mood. When combined, the effects were additive rather than synergistic.

Why it matters

This controlled comparison helps separate what cannabis and alcohol each do to the brain in real time. The finding that cannabis mainly shifts subjective experience while alcohol mainly disrupts performance challenges assumptions that the two substances impair functioning in the same way.

The numbers in context

28 participants completed all four sessions; alcohol target was 80 mg/dL breath alcohol; cannabis was 12.5% THC smoked ad libitum; significant effects found on POMS tension-anxiety and confusion scales, ARCI euphoria and sedation scales, verbal free recall (immediate and delayed), and digit symbol substitution test

How the study worked

Within-subjects, double-blind, double-dummy, placebo-controlled RCT with 28 healthy cannabis users aged 19-29 who had recent binge drinking history. Four conditions tested: placebo/placebo, alcohol/placebo, placebo/cannabis (12.5% THC), and alcohol/cannabis. Cognitive and mood measures taken 75 minutes after alcohol (1 hour after cannabis).

What this study cannot tell us

Small sample of 28 young adults limits generalizability. Single-dose design does not reflect chronic co-use patterns. THC was smoked ad libitum, so doses varied between participants. Only tested one alcohol level and one cannabis potency.

How to read the evidence

Well-designed RCT with placebo control and within-subjects design, but limited by small sample size

When this study was published

2022 study

The bigger picture

As cannabis and alcohol co-use becomes more common, understanding how they interact matters for impairment assessment and driving policy. This study suggests their combined effects on cognition and motor control are driven primarily by alcohol, not cannabis.

Questions still open

Would higher THC concentrations produce more cognitive impairment? Do chronic co-users develop different tolerance patterns for the combined effects? How do these lab findings translate to real-world driving impairment?

Common questions

Does combining cannabis and alcohol make impairment worse than expected?

Not according to this study. The combined effects were additive at most, meaning they added up but did not multiply or create unexpected new impairments.

Which substance caused more cognitive impairment in this study?

Alcohol caused significantly more cognitive and psychomotor impairment than cannabis. Cannabis mainly affected mood and subjective feelings rather than test performance.

Read the original research

Separate and combined effects of alcohol and cannabis on mood, subjective experience, cognition and psychomotor performance: A randomized trial.

Progress in neuro-psychopharmacology & biological psychiatry, 118, 110570

View on PubMed ↗Publisher’s paper ↗

Citation

Wickens, Christine M; Wright, Madison; Mann, Robert E; Brands, Bruna; Di Ciano, Patricia; Stoduto, Gina; Fares, Andrew; Matheson, Justin; George, Tony P; Rehm, Jürgen; Shuper, Paul A; Sproule, Beth; Samohkvalov, Andriy; Huestis, Marilyn A; Le Foll, Bernard. (2022). Separate and combined effects of alcohol and cannabis on mood, subjective experience, cognition and psychomotor performance: A randomized trial.. Progress in neuro-psychopharmacology & biological psychiatry, 118, 110570. https://doi.org/10.1016/j.pnpbp.2022.110570