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Research & Development Neurology & psychology, Adverse effects

Too Much of a Good Thing?

Cannabis may live up to its reputation for reducing stress – but only at the very lowest doses, according to researchers in Chicago (1). Once levels of THC climbed enough to produce a mild “high”, anxiety increased during a psychological stress test.

The scientists divided 42 healthy volunteers, all of whom had tried cannabis but were not regular users, into three groups. The low-dose group received 7.5 mg THC orally, the moderate-dose group received 12.5 mg, while the third group received a placebo pill.

In two separate sessions, the volunteers came to the lab, took their assigned pill and relaxed for two hours before completing various tasks. The first set of tasks, known as the Trier Social Stress Test, was designed to raise stress levels, with a mock interview and a stress test favorite – a math test (counting backwards from a five digit number by subtracting 13). Five days later, the volunteers returned for an easier assignment – talking to lab assistants about a favorite book or movie, then playing solitaire.

Before, during and after each test, participants rated their stress levels and feelings about the tasks, and researchers recorded their blood pressure, heart rate and cortisol levels.

While there were no significant differences in physical signs of stress (blood pressure, etc), participants in the 7.5 mg group reported feeling less anxious than the placebo group during the “stressful” task. However, the 12.5 mg group reported more negative feelings about the test than the other two groups, and showed impaired performance.

The authors concluded: “Our findings suggest that a low dose of THC produces subjective stress-relieving effects in line with those commonly reported among cannabis users, but that higher doses may non-specifically increase negative mood.”


  1. E Childs, JA Lutz, H de Wit, “Dose-related effects of delta-9-THC on emotional responses to acute psychosocial stress”, Drug Alcohol Depend, 177, 136–144 (2017).

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