Researchers from Washington State University in Pullman report their study findings in the journal Psychopharmacology.
First author Carrie Cuttler, a clinical assistant professor of psychology, says, "To the best of our knowledge, this is the first study to examine the effects of acute stress on salivary cortisol levels in chronic cannabis users compared to non-users."
One of the common reasons given for long-term use of marijuana, or cannabis, is that it helps people to cope with stress.
The researchers note that this is supported by evidence that long-term marijuana users have reduced emotional arousal and a blunted stress response when exposed to negative images.
For their study, the team recruited 40 chronic marijuana users and 42 non-users and randomly assigned them to complete either a high-stress version or a no-stress version of a recognized stress test.
This generated four groups: marijuana users and non-users who underwent the high-stress test, and marijuana users and non-users who underwent the no-stress test.
Chronic marijuana use was defined as having used marijuana every day or nearly every day during the past 12 months. Non-use was defined as not having used marijuana more than 10 times ever, or not having used it at all in the past 12 months. All participants were asked to abstain from using marijuana on the day of the stress test.
The stress test, called the Maastricht Acute Stress Test, creates two stress conditions: one physiological and the other psychosocial.
Under the physiological stress condition, participants placed a hand in ice-cold water for up to 90 seconds. In the no-stress condition, the participants put their hand in lukewarm water.
Under the psychosocial stress condition, participants performed mental arithmetic by counting backwards from 2,043 in steps of 17. Throughout the task, they could see themselves on a screen using a video link and also received negative verbal feedback if they made any mistakes. The no-stress groups were just asked to count from 1 to 25.
The participants were asked to rate their stress levels before, during, and after the stress test. The researchers also measured cortisol levels from saliva samples that the participants gave before and afterward.
After the testing was completed, the participants also gave urine samples before they went home. From these, the researchers were able to determine levels of tetrahydrocannabinol, the active substance in marijuana, to confirm the participants' self-reported use of marijuana.
'Blunted stress reactivity'
When they compared the results from the non-users who completed the high-stress with those of the no-stress version of the test, the researchers found that the stress condition produced "significantly higher levels" of self-rated stress and salivary cortisol.
In contrast, the chronic marijuana users showed "blunted stress reactivity," in that there was little difference in the cortisol levels between those who completed the high-stress and the no-stress versions of the test and there was only a small increase in the self-reported stress scores.
Speculating on the findings, the team suggests that using marijuana may increase resilience to stress, particularly in people who have a heightened emotional response under stress.
On the other hand, they also note that the release of cortisol mobilizes energy release that helps us to respond to perceived threats.
Need to investigate 'therapeutic benefits'
Attitudes to marijuana use are changing in the United States, reflected in a relaxation of the law in many states, and in rising use in the population.
Twenty-six states and the District of Columbia have now legalized use of marijuana in some form. Of these, eight have passed laws permitting recreational as well as medicinal use.
The proportion of the population using marijuana in the U.S. more than doubled in the decade leading up to 2013, with 9.5 percent of adults reporting use. Marijuana use is also widespread among teenagers and young adults in the country.
Prof. Cuttler says that their work is not enough to show whether the dampened stress response in long-term marijuana users is a good or a bad thing. However, it does represent "an important first step in investigating potential therapeutic benefits of cannabis at a time when its use is spreading faster than ever before."
The team says that further research is now needed to discover the mechanisms through which use of marijuana blunts the stress response and whether it helps to make people more resilient or more vulnerable.
"Research on cannabis is really just now ramping up because of legalization and our work going forward will play an important role in investigating both the short-term benefits and potential long-term consequences of chronic cannabis use."
Prof. Carrie Cuttler