Acute and delayed effects of THC on memories of stress in healthy adults

Many cannabis users claim that one reason they use cannabis is to relieve stress or dampen effects of stressful memories. However, the processes by which cannabis or its primary constituent, Δ9-tetrahydrocannabinol (THC) alleviate stressful experiences remains unclear. Here, we assessed whether low oral doses of THC reduce emotional or physiological responses to memories of a standardized social stress procedure in healthy volunteers. Healthy adults (18–35 years) received placebo, 5, or 10 mg THC groups (n = 12 per group) under double-blind conditions before retrieving memories of a stressful event. They participated in three sessions: (1) social stress procedure to establish stress memories, (2) pretreatment with THC or placebo followed by presentation of stress session images, and (3) re-presentation of stress images without drug. During Session 1, participants underwent a Trier Social Stress Test (TSST) and a non-stress control task to create individualized stress and neutral memory images. During Session 2 one week later, participants received THC (5 or 10 mg) or placebo before viewing images from Session 1. Dependent measures included subjective and physiological responses to the stress and control images, during a memory retrieval task. During Session 3, conducted one week after Session 2, image-elicited responses were reassessed without administration of drug. During the stress memory retrieval on Session 2, the TSST-images significantly increased distress and arousal relative to control images. However, THC (5 and 10 mg) did not dampen most of the subjective or physiological responses to the images. The only measure on which THC reduced responses was on affective facial emotional expressions during presentation of stress images. No lasting effects of the drug were observed on Session 3. Although the small sample raised questions about power, Bayes factor analyses supported the conclusion of null findings. Using this novel procedure, images established with a social stress procedure elicited stress responses one week later. However, low doses of THC failed to diminish most of the subjective or physiological responses to stress-related images. Future work should examine whether these findings can be replicated in larger samples.