Although cannabinoids were found to improve the pain experience in individuals subjected to experimental pain — by reducing the associated feeling of unpleasantness and improving tolerability — they were not found to have analgesic effects on existing experimental pain, suggesting that these agents may modulate affective processes, according to a systematic review and meta-analysis published in JAMA Psychiatry.

Clinical trials databases were searched for placebo-controlled studies in which cannabinoids were administered to healthy patients (18 trials and 442 participants). Data were extracted and pooled to generate summary estimates that included study characteristics, cannabinoid doses and types, gender composition, and outcomes. The main outcomes and measures were experimental pain threshold, pain intensity, pain tolerance, pain unpleasantness, and mechanical hyperalgesia.

The administration of cannabinoids was associated with modest increases in pain threshold (effect sizes estimated using Hedges g factor: g=0.186; 95% CI, 0.054-0.318; P =.006), small to medium increases in pain tolerance (g=0.225; 95% CI, 0.015-0.436; P =.04), and small to medium reductions in the unpleasantness of current experimental pain (g=0.288; 95% CI, 0.104-0.472; P =.002). Cannabinoids were not associated with reduced experimental pain intensity (g=0.017; 95% CI, −0.120-0.154; P =.81) or mechanical hyperalgesia (g=0.093; 95% CI, −0.059-0.244; P =.23).

 “Meta-analyses revealed that although the cannabinoids examined in this review may prevent the onset of laboratory-induced pain by increasing pain thresholds, they do not appear to reduce the intensity of experimental pain that is already being experienced,” the investigators wrote. “Instead, these substances make experimental pain feel less unpleasant and more tolerable, suggesting a notable influence on affective processes.”

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Reference

De Vita MJ, Moskal D, Maisto SA, Ansell EB. Association of cannabinoid administration with experimental pain in healthy adults: A systematic review and meta-analysis. JAMA Psychiatry. 2018;75(11):1118-1127.