Alcohol and Marijuana Produced Similar Impairment on Memory and Processing Tasks at Comparable Doses
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.
Quick Facts
What This Study 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.
Key Numbers
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 They Did This
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.
Why This Research 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 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.
What This Study Doesn't 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.
Questions This Raises
- ?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?
Trust & Context
- Key Stat:
- Perceived impairment was identical for high-dose alcohol and marijuana
- Evidence Grade:
- A well-controlled double-blind within-subjects design, but with only five participants severely limiting statistical power and generalizability.
- Study Age:
- Published in 1997. The marijuana used was 3.55% THC, roughly one-sixth the potency of today's typical products.
- Original Title:
- Comparative effects of alcohol and marijuana on mood, memory, and performance.
- Published In:
- Pharmacology, biochemistry, and behavior, 58(1), 93-101 (1997)
- Authors:
- Heishman, S J, Arasteh, K, Stitzer, M L
- Database ID:
- RTHC-00060
Evidence Hierarchy
Participants are randomly assigned to treatment or placebo groups to test cause and effect.
What do these levels mean? →Frequently Asked 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.
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Cite This Study
https://rethinkthc.com/research/RTHC-00060APA
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.
MLA
Heishman, S J, et al. "Comparative effects of alcohol and marijuana on mood, memory, and performance.." Pharmacology, 1997.
RethinkTHC
RethinkTHC Research Database. "Comparative effects of alcohol and marijuana on mood, memory..." RTHC-00060. Retrieved from https://rethinkthc.com/research/heishman-1997-comparative-effects-of-alcohol
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkTHC research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.