Participants in a new study reported feeling less stressed after vaping cannabis, but also reported the same reduction in stress when they were unknowingly given a placebo containing no THC.
Published in the journal Neuropsychopharmacology, researchers from Washington State University and Arizona State University recruited 120 regular cannabis users for the randomised, double-blind study.
Participants were randomly asked to vape cannabis containing either 20mg or 40mg of tetrahydrocannabinol (THC), or a placebo containing no THC. Neither the participants nor researchers administering the cannabis knew who had received which product.
Participants rated how stressed they felt before vaping, five minutes afterwards and again after an hour. Researchers also took saliva samples to measure cortisol, a hormone released in response to stress, and participants wore wristbands measuring heart rate, heart rate variability (HRV) and changes in electrical activity in the skin.
People in all three groups reported feeling less stressed after vaping. Crucially, however, the reduction among people who received THC was no greater than among those given the placebo.
“Consumers should understand that while they feel like cannabis is reducing their stress, that could largely be a kind of placebo effect, due to their expectations of what they think cannabis is going to do,” said lead author Carrie Cuttler.
Researchers suggest the findings point towards an expectancy effect: participants may have felt more relaxed because they expected cannabis to make them feel that way, rather than as a direct consequence of THC.
Cortisol initially fell across all three groups, with a larger decrease among participants given 40mg of THC. Levels subsequently increased again in both THC groups. Some measurements of electrical activity in the skin, another indicator associated with physiological arousal, also fell following THC consumption.
However, heart rate moved in the opposite direction. Participants given the higher THC dose experienced a significantly greater increase in heart rate than those receiving the placebo. Cannabis had no detectable effect on heart rate variability.
Researchers conclude that the use of cannabis affects different parts of the stress response in different ways and that people’s perception of cannabis as a stress reliever does not necessarily reflect a uniform reduction in physiological stress. The findings are particularly relevant given that reducing stress is a common reason for consuming cannabis.
Previous research by some of the same Washington State University researchers has also found differences in how regular cannabis users respond to stress. A 2017 study involving 40 regular cannabis users and 42 non-users found that regular users showed a blunted response when subjected to an acute stress test, including a smaller increase in self-reported stress.
Cannabis can also have markedly different effects depending on the cannabinoid being studied. Research also led by Carrie Cuttler in 2024 found that 20mg of cannabigerol (CBG) reduced self-reported anxiety and stress compared with a placebo, without producing the intoxication associated with THC.
The authors of the recent study noted that the design had some limitations: All 120 participants were regular cannabis users, meaning the results cannot necessarily be applied to people who rarely or never consume cannabis. The experiment also examined the immediate effects of two substantially high doses of THC rather than the effects of different cannabis products, cannabinoid ratios or patterns of long-term use.
“It’s not a consistent story. Cannabis has different effects depending on the outcome that you’re looking at,” the authors concluded.
