Alcohol and Marijuana Produced Similar Impairment on Memory and Processing Tasks at Comparable Doses | Research

The takeaway

When controlling for dose delivery, high-dose alcohol and marijuana produced identical perceived impairment and comparable deficits on digit-symbol and word recall tasks, though neither affected reaction time.

Read this if you want a direct comparison of how alcohol and marijuana affect cognitive performance at controlled doses.

Perceived impairment was identical for high-dose alcohol and marijuana

What the researchers found

Five male volunteers received three doses each of alcohol and marijuana under double-blind conditions across seven sessions, using technology that controlled puffing and inhalation parameters for precise marijuana dosing.

At the highest doses, perceived impairment was identical for alcohol and marijuana. Both drugs comparably impaired digit-symbol substitution (a measure of processing speed) and word recall (memory). Neither drug affected time perception or reaction time.

Alcohol slightly impaired number recognition performance while marijuana did not, representing the only clear difference between the two drugs.

Blood alcohol concentrations ranged from 10-90 mg/dL, while THC levels reached 63-188 ng/mL, confirming dose-dependent drug delivery.

Why it matters

By using controlled dosing for both substances, this study enabled the first precise comparison of alcohol and marijuana impairment profiles. The finding of similar impairment patterns challenges the common assumption that one substance is inherently more impairing than the other.

The numbers in context

Five subjects, seven sessions. Alcohol: 0.25-1.0 g/kg (BAC 10-90 mg/dL). Marijuana: 4-16 puffs of 3.55% THC (blood THC 63-188 ng/mL). Identical perceived impairment at high doses.

How the study worked

Double-blind, placebo-controlled, within-subjects design with 5 male volunteers. Three doses each of alcohol (0.25, 0.5, 1.0 g/kg) and marijuana (4, 8, 16 puffs of 3.55% THC). Controlled puffing technology for marijuana. Measures included subjective ratings, digit-symbol substitution, word recall, number recognition, time perception, and reaction time.

What this study cannot tell us

Only five male participants. Controlled laboratory conditions do not reflect real-world use patterns. The marijuana used (3.55% THC) is substantially weaker than modern products. The narrow range of cognitive tests may miss domain-specific differences.

How to read the evidence

A well-controlled double-blind within-subjects design, but with only five participants severely limiting statistical power and generalizability.

When this study was published

Published in 1997. The marijuana used was 3.55% THC, roughly one-sixth the potency of today's typical products.

The bigger picture

This study established that when dosing is carefully controlled, alcohol and marijuana produce remarkably similar patterns of cognitive impairment. This finding is relevant to debates about relative harm and about how driving impairment laws should treat the two substances.

Questions still open

Would the comparison hold with modern high-potency marijuana? Do the impairment profiles diverge at higher doses or during different tasks? How do the recovery timelines compare between the two substances?

Common questions

Is marijuana as impairing as alcohol?

In this controlled comparison, high-dose marijuana and alcohol produced identical perceived impairment and similar deficits on memory and processing tasks. The only difference was that alcohol slightly impaired number recognition.

Did marijuana affect reaction time?

No. Neither marijuana nor alcohol affected reaction time at the doses tested, though both impaired digit-symbol substitution and word recall.

Read the original research

Comparative effects of alcohol and marijuana on mood, memory, and performance.

Pharmacology, biochemistry, and behavior, 58(1), 93-101

View on PubMed ↗

Citation

Heishman, S J; Arasteh, K; Stitzer, M L. (1997). Comparative effects of alcohol and marijuana on mood, memory, and performance.. Pharmacology, biochemistry, and behavior, 58(1), 93-101.