Mixing Marijuana and Amphetamines: Heart Effects Added Up but Cognitive Impairment Came from the Weed
Combining marijuana and dextroamphetamine produced additive increases in heart rate and blood pressure, but psychomotor impairment was driven entirely by marijuana with no additional effect from the stimulant.
Quick Facts
What This Study Found
In two double-blind, randomized studies, researchers tested the combination of marijuana and dextroamphetamine. Heart rate and blood pressure increases were additive when both drugs were taken together. EKG changes were nonspecific and associated with marijuana.
For cognitive and motor performance, impairment tracked with marijuana only. Adding amphetamine to marijuana did not worsen or improve psychomotor performance compared to marijuana alone. Subjective effects measured by a modified symptom questionnaire also showed only additive patterns, with no synergistic interaction.
Key Numbers
- Amphetamine dose: 10 mg/70 kg
- THC dose: 50 mcg/kg (Study 1), 25 mcg/kg (Study 2)
- Heart rate and blood pressure: additive effects from combination
- Psychomotor impairment: attributable to marijuana only
- Subjective effects: additive, no synergistic interaction
How They Did This
Two separate double-blind, randomized, complete block design studies. Study 1: placebo or 10 mg/70 kg dextroamphetamine orally, followed 1.5 hours later by a marijuana cigarette delivering 50 mcg/kg THC. Cardiovascular measures tracked. Study 2: same amphetamine dose with marijuana delivering 25 mcg/kg THC. Psychomotor performance evaluated.
Why This Research Matters
This is one of the earliest controlled drug interaction studies involving cannabis. The finding that cardiovascular effects were additive but cognitive effects were not is practically important for understanding polydrug use. It suggested that mixing cannabis with stimulants increases cardiac strain without counteracting the mental impairment from cannabis.
The Bigger Picture
People who use cannabis with stimulants (amphetamines, cocaine, ADHD medications) often assume the stimulant will offset the cognitive impairment from cannabis. This study suggested otherwise: the heart bears the combined load of both drugs while the brain stays impaired by the cannabis regardless of the stimulant.
What This Study Doesn't Tell Us
Small sample size (not specified in abstract). Only one dose combination was tested in each study. Short-term, single-session design. Conducted in the 1970s with lower-potency cannabis than is available today. The amphetamine dose was relatively low.
Questions This Raises
- ?Would higher stimulant doses overcome cannabis-induced psychomotor impairment?
- ?Does the additive cardiovascular effect pose clinical risks for people with heart conditions who use both substances?
Trust & Context
- Key Stat:
- Additive cardiac load heart rate and blood pressure increased from both drugs combined, but cognition was impaired by marijuana alone
- Evidence Grade:
- Randomized, double-blind design but small sample size and single-session exposure. Preliminary evidence for drug interaction effects.
- Study Age:
- Published in 1976. One of the first controlled cannabis-stimulant interaction studies. The core finding remains relevant for understanding polydrug cardiovascular risk.
- Original Title:
- Effects of marihuana-dextroamphetamine combination.
- Published In:
- Clinical pharmacology and therapeutics, 20(3), 350-8 (1976)
- Authors:
- Evans, M A, Martz, R(2), Rodda, B E, Lemberger, L, Forney, R B
- Database ID:
- RTHC-00010
Evidence Hierarchy
Participants are randomly assigned to treatment or placebo groups to test cause and effect.
What do these levels mean? →Read More on RethinkTHC
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Cite This Study
https://rethinkthc.com/research/RTHC-00010APA
Evans, M A; Martz, R; Rodda, B E; Lemberger, L; Forney, R B. (1976). Effects of marihuana-dextroamphetamine combination.. Clinical pharmacology and therapeutics, 20(3), 350-8.
MLA
Evans, M A, et al. "Effects of marihuana-dextroamphetamine combination.." Clinical pharmacology and therapeutics, 1976.
RethinkTHC
RethinkTHC Research Database. "Effects of marihuana-dextroamphetamine combination." RTHC-00010. Retrieved from https://rethinkthc.com/research/evans-1976-effects-of-marihuanadextroamphetamine-combination
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.