Extended daily THC use reversed the typical heart rate increase seen with single doses, instead slowing heart rate and lowering blood pressure in hospitalized volunteers.
Read this if you use cannabis daily and want to understand how your cardiovascular response changes from occasional to regular use.
Biphasic effectSingle-dose THC speeds heart rate; prolonged use slows it
What the researchers found
Single doses of THC speed up heart rate and raise blood pressure. But when hospitalized volunteers took THC continuously over an extended period, the opposite happened: heart rate slowed and blood pressure dropped.
The researchers observed impaired circulatory responses to standing, exercise, and cold exposure, pointing to reduced sympathetic nervous system activity. All subjects gained substantial weight during the study, linked to fluid retention and plasma volume expansion.
Tolerance developed to the drop in blood pressure upon standing (possibly from the expanded blood volume), but blood pressure while lying down stayed low throughout. The psychological high and heart rate increase from smoked marijuana also diminished almost completely during ongoing THC intake.
Why it matters
This 1975 study was among the first to document that THC has opposite cardiovascular effects depending on whether exposure is acute or chronic. The finding that the body adapts to some effects (heart rate increase, orthostatic hypotension) but not others (sustained blood pressure lowering) shaped decades of follow-up research on cannabis tolerance and cardiovascular safety.
The numbers in context
- Heart rate: tachycardia with single doses reversed to bradycardia with prolonged use
- Blood pressure: significant lowering in supine position persisted without tolerance
- Tolerance to psychological effects of smoked marijuana developed nearly completely
- All subjects experienced marked weight gain from fluid retention
How the study worked
Hospitalized volunteers received prolonged oral THC in a controlled clinical setting. Researchers tracked heart rate, blood pressure, circulatory responses to physical challenges (standing, exercise, cold pressor test, Valsalva maneuver), weight changes, and electrocardiogram readings throughout the study period.
What this study cannot tell us
The study used a small number of hospitalized volunteers in a controlled setting that does not reflect real-world cannabis use. Only oral THC was administered for the prolonged phase. The specific doses and duration are not detailed in the abstract. Results from the 1970s may not directly apply to modern cannabis products with different potency and delivery methods.
How to read the evidence
Small observational study in hospitalized volunteers without a control group. Provides preliminary clinical observations but limited generalizability.
When this study was published
Published in 1975. One of the earliest controlled studies on prolonged THC cardiovascular effects. Foundational for the field but predates modern cannabis products.
The bigger picture
This study introduced a key concept still relevant today: THC appears to have biphasic effects on the sympathetic nervous system, stimulating it acutely but suppressing it with extended use. Understanding this pattern matters for anyone using cannabis regularly, as the cardiovascular profile shifts fundamentally from short-term to long-term exposure.
Questions still open
- Does the blood pressure lowering from extended THC use persist after stopping, or does it reverse?
- Do modern high-potency cannabis products produce the same biphasic cardiovascular pattern?
- Could the fluid retention and weight gain pose risks for people with heart failure or kidney disease?
Read the original research
Cardiovascular effects of prolonged delta-9-tetrahydrocannabinol ingestion.
Clinical pharmacology and therapeutics, 18(3), 287-97
Citation
Benowitz, N L; Jones, R T. (1975). Cardiovascular effects of prolonged delta-9-tetrahydrocannabinol ingestion.. Clinical pharmacology and therapeutics, 18(3), 287-97.
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