Neurophysiological and Behavioural Effects of Combined Cannabis Concentrates and Alcohol Among People Who Regularly Use Alcohol and Cannabis.

Hetelekides E.; Davies P.; Prince M.; Gavin W.; Karoly H. · Addiction biology · 2026

**Background & Methods** This naturalistic feasibility study examined acute neurophysiological and behavioral effects of combined alcohol and cannabis concentrate use in 17 heavy-drinking, regular cannabis users (mean age 31.7 years, 65% male). Participants underwent electroencephalography (EEG) during a speeded visual-flanker performance monitoring task at three timepoints: baseline (sober), 1-hour post co-consumption (intoxicated), and 4-hours post co-consumption (recovery), with standardized doses of alcohol and a THC-concentrated cannabis product administered between baseline and intoxicated assessments. **Key Findings** - **Behavioral impairment during co-intoxication:** At the intoxicated timepoint, participants demonstrated significantly increased error rates (p<0.005, η²p=0.35) and decreased response times (p<0.001, η²p=0.50), indicating greater impulsivity compared to sober and recovery periods. - **Diminished neural processing:** Event-related potential components measuring cognitive function showed significantly reduced amplitudes during intoxication across stimulus-locked measures (P2, N2, P3) and response-locked measures (error-related negativity and error positivity), indicating impaired decision-making, error detection, and performance monitoring. - **Incomplete recovery:** Both performance and neurophysiological measures remained diminished at the 4-hour recovery timepoint compared to baseline, suggesting prolonged cognitive impairment beyond acute intoxication. **Dosage & Administration** Standardized doses of alcohol and cannabis concentrate product were administered, though specific quantities are not detailed in the abstract. **Safety & Adverse Effects** Not reported. **Evidence Quality** This study has significant limitations as a naturalistic feasibility trial with a small sample size (N=17), limiting generalizability. The lack of randomization, control conditions, and blinding reduces internal validity. The study provides preliminary evidence of acute co-intoxication effects but cannot establish causal mechanisms. While EEG provides objective neurophysiological measurement, the single 4.5-hour observation window may not capture full recovery trajectories. Findings are most applicable to heavy alcohol and cannabis users and may not generalize to occasional or moderate users. The study's relevance to real-world activities like driving warrants further investigation with larger, more rigorous designs.

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