HealthDay News — The cannabis constituent Δ9-tetrahydrocannabinol (THC) administration can induce psychotic, negative, and other psychiatric symptoms in healthy adults, according to a review published online March 17 in The Lancet Psychiatry.

Guy Hindley, M.B.B.S., from King’s College London, and colleagues conducted a systematic review and meta-analysis to examine the effect of the THC alone and in combination with cannabidiol (CBD) compared with placebo for psychiatric symptoms among healthy people. Fifteen eligible studies involving the acute administration of THC and four on CBD plus THC administration were reviewed.

The researchers found that THC increased total symptom severity with a large effect size (standardized mean change [SMC], 1.10; 95 percent confidence interval [CI], 0.92 to 1.28; P < 0.0001), increased positive symptom severity (SMC, 0.91; 95 percent CI, 0.68 to 1.14; P < 0.0001), and increased negative symptom severity with a large effect size (SMC, 0.78; 95 percent CI, 0.59 to 0.97; P < 0.0001) compared with placebo. Only one of the four studies evaluating CBD’s effects on THC-induced symptoms identified a significant reduction in symptoms.

“Our finding that THC can temporarily induce psychiatric symptoms in healthy volunteers highlights the risks associated with the use of THC-containing cannabis products,” a coauthor said in a statement. “This potential risk should be considered in discussions between patients and medical practitioners thinking about using cannabis products with THC.”


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One author disclosed financial ties to the biopharmaceutical industry.

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