Researchers at Washington State University report that rats with naturally higher baseline stress hormone levels are far more likely to self-administer cannabis vapor. In experiments described in Neuropsychopharmacology, resting stress hormones emerged as the strongest predictor of this drug-seeking behavior, suggesting potential early markers of vulnerability to problematic use.
A research team led by Ryan McLaughlin, an associate professor in Washington State University's College of Veterinary Medicine, examined why some rats actively seek out cannabis when given the opportunity.
Over the course of three weeks, the rats were observed for one hour a day in an air‑tight chamber where they could choose to inhale cannabis vapor. By poking their noses into a vapor port, they triggered a three‑second burst of cannabis vapor, a behavior researchers tracked as "nose‑pokes".
According to Washington State University and related reports on the study, McLaughlin's team put the animals through an extensive battery of behavioral and biological tests. They assessed traits such as social behavior, sex, cognition, reward sensitivity and arousal to build a behavioral profile for each rat.
The scientists measured levels of corticosterone, the primary stress hormone in rats and the equivalent of cortisol in humans. They found that rats with higher natural, or baseline, corticosterone levels were far more likely to self‑administer cannabis and logged more frequent nose‑pokes. In the words of McLaughlin, "stress levels seem to matter the most when it comes to cannabis use."
Crucially, it was the rats' resting baseline stress levels that were associated with cannabis self‑administration, not hormone spikes caused by an acute stressor such as a challenging task. When stress hormone levels were examined after exposure to a stressor, they did not show a significant link to cannabis‑seeking behavior.
The study also identified significant relationships between rates of cannabis self‑administration and measures of "cognitive flexibility," the ability to adapt to changing rules. Animals that were less flexible when shifting between rules during cognitive testing tended to show stronger cannabis‑seeking behavior. McLaughlin noted that rats relying more heavily on visual cues to guide their decision‑making were among the most highly motivated to obtain cannabis vapor.
In addition, the researchers found a weaker but detectable association between cannabis self‑administration and a combination of high morning corticosterone and low levels of endocannabinoids, naturally occurring compounds that help maintain physiological balance. The authors suggest that low endocannabinoid tone, together with high baseline stress hormones, may further increase motivation to seek cannabis.
McLaughlin has linked these findings to human patterns of use, pointing out that coping with stress is one of the most commonly reported reasons for habitual cannabis consumption. He said that baseline stress measures could one day contribute to screening tools. "Our findings highlight potential early or pre‑use markers that could one day support screening and prevention strategies," he said. "I could certainly envision a scenario where having an assessment of baseline cortisol might provide some level of insight into whether there's an increased propensity for you to develop problematic drug use patterns later in life."
As more jurisdictions decriminalize or legalize cannabis, the authors argue that understanding how stress, cognitive traits and endocannabinoid biology shape drug‑seeking behavior is increasingly important. While the work was conducted in rats, the patterns they uncovered could help inform future research into individual vulnerability to cannabis misuse in people.
