Reuters Health News | September 28, 2018
Cannabinoid drugs may reduce or prevent pain by producing small increases in pain thresholds, rather than by reducing the intensity of experimental pain that is already being experienced, researchers say.
“We meta-analyzed the results from every available experimental pain trial, and found that numerous aspects of pain were being influenced in different ways,” Martin DeVita of Syracuse University in New York told Reuters Health.
“Although cannabinoids increased pain thresholds, they did not appear to reduce the intensity of ongoing pain (sensory dimension),” he said by email. “However, cannabinoids made pain feel less unpleasant (affective dimension) and more tolerable. These findings suggest that cannabinoids may have a notable influence on the emotional component of pain.”
DeVita and colleagues searched the literature from inception through September 2017 for studies of healthy adults who had experimentally controlled administration of any cannabinoid preparation in a quantified dose for laboratory-induced acute pain. Studies including participants with chronic pain were excluded.
As reported online September 19 in JAMA Psychiatry, the team identified 18 placebo-controlled studies including 442 participants, about half of whom were men. Participants in 13 of the studies had a mean age of about 27; four reported an age range from 21 to 30 and one reported a median age of about 23.
The search yielded sufficient data to analyze 18 pain threshold comparisons, 22 pain intensity comparisons, 9 pain unpleasantness comparisons, 13 pain tolerance comparisons, and 9 mechanical hyperalgesia comparisons.
Pooling effect sizes revealed that cannabinoid administration was associated with small increases in pain threshold, meaning that greater amounts of stimulation were required to induce pain after cannabinoid administration.
Small- to medium-sized reductions were seen in the perceived unpleasantness of ongoing experimental pain after cannabinoid administration, suggesting, as DeVita noted, that cannabinoids may influence an affective dimension of pain.
A similar association was shown for pain tolerance, meaning participants were able to withstand more pain after cannabinoid administration. Further analyses indicated that the association of cannabinoids with both pain unpleasantness and pain tolerance was stronger for plant-based cannabis than for synthetic cannabinoids.
By contrast, cannabinoid administration was not associated with a decrease in pain intensity or mechanical hyperalgesia.
“Cannabis-induced improvements in pain-related negative affect may underlie the widely held belief that cannabis relieves pain,” the authors state.
“If anything, our findings indicate that the analgesic properties of cannabinoid drugs are much more complex than we originally thought,” DeVita said. “We are just beginning to understand these complexities, and there are more questions in need of answering. For example, it is unclear whether tolerance in regular cannabis users would reduce analgesic effects from cannabinoids.”
“When considering treatment planning and goals,” he added, “patients and clinicians should consider whether the intoxicating effects of psychoactive cannabinoids would offset improvements in functioning as well.”
“Either way,” he concluded, “we need to continue building our evidence base.”
Dr. M. Fahad Khan, assistant professor at NYU Langone’s Center for the Study and Treatment of Pain, commented by email, “The study attempts to make the conclusion that rather than actually helping lower pain, cannabinoids may instead simply make the pain experience more tolerable from the patient perspective.”
“If this is true, doctors should not be counseling patients that cannabinoids will take away your pain,” he said. “Instead, they should probably be telling them, ‘You may still feel pain … but it just won’t be as unpleasant.'”
Further, he noted, “the experimental pain model they were studying was an acute pain model. Most cannabinoids prescribed today are being written for chronic pain. The results might not apply to the chronic pain population.”
“Most people think that cannabinoids are likely going to be of most benefit in neuropathic pain conditions,” he added. “The experimental pain condition created in the studies pooled in this paper created a mechanical or nociceptive pain condition in order to study the drug effects. Therefore, the ability to generalize the results of this study to the patient population in whom cannabinoids would be considered to work best is likely limited.”
—Marilynn Larkin