People who use marijuana heavily have reactions to anxiety-inducing stimuli that resemble those of people diagnosed with anxiety disorders, according to a study to be published in the journal Addictive Behaviors Reports.

Psychological tests of people’s reactions to threatening and non-threatening pictures have shown that people with anxiety disorders exhibit a pattern of eye movements that differs from people without these disorders. Those suffering from anxiety disorders have a tendency to focus their eyes on threatening images for shorter lengths of time, compared with others, a phenomenon known as attentional bias. For example, people with specific phobias fix their eyes for less time on images of the objects they fear.

Although the lengths of time involved in these assessments are measured in nanoseconds, psychologists believe that they reveal a tendency to avoid processing information about anxiety-inducing stimuli, which may be counterproductive for overcoming these fears.

Two researchers, Thomas Wilcockson of Lancaster University, and Nilihan Sanal, of Swansea University, examined attitudinal bias among eight daily marijuana users and 15 control participants who had never used the drug. All participants performed an experimental task in which they were briefly shown two pictures simultaneously, one of which contained a small dot.

The participants had to identify which picture contained the dot as quickly as possible. While they were performing this task, their eye movements were monitored by cameras to determine how quickly and for how long of a duration their eyes fixed on each image. Each pair contained one image that was threatening (for example, a rattlesnake) and one that was emotionally neutral (for example, a book). Participants were also assessed for symptoms of anxiety.

Results of the eye monitoring tests indicated that the heavy marijuana users spent significantly less time fixing their eyes to the threatening images than to the neutral images. The control participants did not exhibit this attitudinal bias. This pattern is similar to that which has been found in studies comparing people suffering from anxiety disorders with controls. There were no differences between the two groups in terms of anxiety symptoms, however, suggesting that any anxiety impact that marijuana use may have had took place at the level of implicit processing, rather than on a conscious level.

The study authors conclude that the presence of attitudinal biases related to anxiety-inducing stimuli may suggest that heavy marijuana use has the potential to increase the risk of developing an anxiety disorder. Alternatively, they suggest it is possible that some people prone to anxiety disorders may engage in heavy marijuana use as a means of self-medicating. In either case, marijuana users and mental health professionals may want to take note of these potential links when it comes to assessing risk for anxiety disorders.