Rats with elevated levels of stress hormones at rest and reduced cognitive flexibility showed a significantly higher motivation to seek out cannabis vapor.

A study conducted by researchers at Washington State University revealed that not only humans, but also rats, may use cannabis to cope with stress when given the opportunity.

Research Goals and Process

In a paper published in the journal Neuropsychopharmacology, the researchers aimed to determine which animals would actively seek out cannabis and for what reasons. They found that rats with initially higher stress levels were more likely to self-administer this commonly used recreational substance. According to Ryan McLaughlin, an associate professor at the WSU College of Veterinary Medicine, among all the factors studied, stress level was the most significant predictor of cannabis use.

Experimental Methodology

To identify which traits influence the tendency to use cannabis, McLaughlin’s team conducted a comprehensive study, evaluating a wide range of characteristics: social behavior, sex, cognitive abilities, reward sensitivity, and arousal level. Based on these data, they created a behavioral profile for each rat.

For three weeks, the animals were observed daily for an hour. During this time, the rats could self-administer cannabis vapor by inserting their noses into a special port that released a three-second burst of vapor into a sealed chamber. Students recorded how many times each rat used the port and then compared this data to their baseline stress hormone levels. The results showed that rats making more attempts had higher initial levels of stress hormones.

The Role of Hormones and Cognitive Traits

The researchers measured the rats’ levels of the stress hormone corticosterone, which is analogous to human cortisol. Animals with naturally higher corticosterone levels were more likely to self-administer cannabis. McLaughlin explained that baseline stress hormone levels can predict the frequency of self-administration, which aligns with observations in humans, where stress relief is a primary reason for regular cannabis use.

The key factor was the baseline stress level, not short-term spikes caused by physical exertion or mental tasks. Hormone measurements taken after exposure to stressors did not show a significant link to cannabis-seeking behavior.

Cognitive Flexibility and Motivation

The study also found a strong correlation between the frequency of self-administered cannabis use and performance on cognitive flexibility tests—the ability to adapt when rules or conditions change. Animals that struggled to switch between rules in cognitive tests were more likely to seek out cannabis. Rats that relied more on visual cues when making decisions were also the most motivated to self-administer cannabis vapor.

Additional Biochemical Factors

Beyond baseline stress levels, the researchers discovered another pattern: a combination of high morning corticosterone and low endocannabinoid levels was also associated with cannabis use, though this link was weaker than the influence of baseline stress. Endocannabinoids are compounds produced by the body to help maintain internal balance (homeostasis).

McLaughlin suggested that people may be more inclined to use cannabis if THC acts as a substitute for endocannabinoids in those with lower natural levels, which could explain the drive to compensate for this deficiency with cannabis.

Significance of the Findings

As more states decriminalize and legalize recreational cannabis, McLaughlin emphasized the importance of understanding how this substance affects the brain and behavior, as well as how patterns of misuse develop.

According to him, the results point to potential early or pre-use markers that could help with future screening and prevention. For example, assessing baseline cortisol levels might provide insight into an individual’s risk for developing problematic patterns of drug use.