Population studies have consistently shown men to use cannabis more frequently than women and seek out treatment for cannabis use more often than women. However, a growing number of women report using cannabis for medical purposes, and this underscores the importance of exploring potential sex differences in the plant’s therapeutic effects.
This area has largely gone unexplored by experimental studies. Animal studies using rats, however, have found sex differences, with female rats being more sensitive to cannabis’ analgesic effects for both acute and chronic pain. And now, a study published in October 2016 in the Drug and Alcohol Dependence journal provides insight as to whether these sex differences translate to humans.
To do this, researchers Ziva D. Cooper and Margaret Haney from Columbia University took 42 regular cannabis smokers (half men, half women) and gave them cannabis containing either 0.00% or 3.56-5.60% THC. After smoking, they underwent a Cold Pressor Test (CPT) to evaluate their pain tolerance and sensitivity.
The CPT involves immersing a participant’s hand in very cold water and measuring pain sensitivity by how long it takes them to report feeling any pain, and pain tolerance by how much time passes before they withdraw their hand from the cold water. This test has previously been used to evaluate the efficacy of opioid analgesics and to demonstrate the analgesic effects of both smoked cannabis and oral THC.
The results uncovered a significant difference in how effective cannabis was as an analgesic for men and women. Men showed a large decrease in pain sensitivity following smoking, as well as an increase in pain tolerance. Women, on the other hand, experienced no change to pain sensitivity and only a small increase in tolerance.
The researchers also assessed how bothersome the pain was and several subjective effects of cannabis but found no sex differences.
Two major limitations were noted in this study. The first is that only regular cannabis smokers were evaluated, so it is not yet clear if this difference is generalizable to light smokers or non-smokers. Animal studies have shown that female rats acquire greater tolerance to the analgesic effects of THC, and if this difference is also seen in humans, then the sex difference may be attributable to the female participants having a stronger tolerance to cannabis than the male participants. Studies on lighter smokers and non-smokers should help to clarify this point.
The second limitation is that the CPT is the only pain stimulus that was used. Future studies using mechanical, heat, or chemical-induced pain will help to better understand if this difference is stable across various kinds of pain stimuli.
The findings of this study stress the need for cannabis researchers to include an analysis of sex differences in the design of future studies. And if these findings are found to be replicable across different populations and pain conditions, health professionals prescribing cannabis will have to take these differences into consideration when deciding on strains and dosage for their patients.
Interested readers can find the full study here.