De Vita MJ, et al. - Researchers investigated the link between cannabinoid drug administration and experimental pain outcomes in healthy adults via a systematic review and meta-analysis of the relevant studies. They noted that small increases in pain thresholds resulted from cannabinoid drug administration, and this could prevent the onset of pain. However, the intensity of experimental pain already being experienced could not be attenuated. An impact of cannabinoids on affective processes was suggested by the observation that cannabinoids could make experimental pain feel less unpleasant and more tolerable. Data suggested that improvements in pain-related negative affect induced by cannabis might be the basis of the widely held belief that cannabis relieves pain.

Methods

• PubMed, EMBASE, MEDLINE, PsycINFO, and CINAHL were systematically searched from the inception of each database to September 30, 2017 for studies that included healthy participants and an experimentally controlled administration of any cannabinoid preparation in a quantified dose; researchers excluded studies that used participants with chronic pain.
• They extracted information on study characteristics, cannabinoid types and doses, sex composition, and outcomes.
• They used a validity measure previously established in published reviews to evaluate study quality.
• They pooled data and generated summary estimates, using random-effects meta-analyses.
• Experimental pain threshold, pain tolerance, pain intensity, pain unpleasantness, and mechanical hyperalgesia were the main outcomes and measures.

Results

• They identified a total of 18 placebo-controlled studies [with 442 participants, 233 (52.7%) were male and 209 (47.3%) were female].
• For sample ages, a mean sample age (26.65 years) was reported by 13 (72%) of the 18 studies, 4 (22%) reported a range, and 1 (6%) reported a median value.
• Analysis of 18 pain threshold comparisons, 22 pain intensity comparisons, 9 pain unpleasantness comparisons, 13 pain tolerance comparisons, and 9 mechanical hyperalgesia comparisons was possible with the sufficient data obtained via the search.
• In association with cannabinoid administration, small increases in pain threshold (Hedges g=0.186; 95% CI, 0.054-0.318; P=.006), small to medium increases in pain tolerance (Hedges g=0.225; 95% CI, 0.015-0.436; P=.04), and a small to medium reduction in the unpleasantness of ongoing experimental pain (Hedges g=0.288; 95% CI, 0.104-0.472; P=.002) were observed.
• The association of cannabinoid administration with a decrease in experimental pain intensity (Hedges g=0.017; 95% CI, -0.120 to 0.154; P=.81) or mechanical hyperalgesia (Hedges g = 0.093; 95% CI, -0.059 to 0.244; P=.23) was not reliable.
• A good mean quality rating across studies was found.