Does long-term cannabis use increase sensitivity to pain in the same way opioids do? According to the Journal of Pain Research, an estimated 20% of the human population suffers from chronic pain. Pharmacological therapies are the default for managing chronic pain, and until recently, opioids were favored “as part of a wider strategy to improve pain management” in the United States. However, this strategy led to the opioid epidemic. With the CDC and medical practitioners across the country sounding the alarm about opioid abuse and addiction, cannabis is becoming an increasingly attractive option to treat chronic painWhile dependence and overdose are well-known risks of opioid drugs, the fact that long-term opioid use actually increases people’s sensitivity to pain is less known. This increased sensitivity to acute pain, known as hyperalgesia, is one reason that people who are prescribed opioids often need to increase their dose. Tolerance is the other reason. As the dose goes up, patients’ tolerance also goes up, while at the same time they get more sensitive to pain. Opioid-induced hyperalgesia creates a vicious cycle that puts patients at increased risk of addiction or overdose. It is thought that cannabinoids and opioids reduce pain by interacting with the nervous system in similar ways. Does long-term cannabis use carry the same risk of hyperalgesia?
A recent study led by Michelle St. Pierre, a doctoral student at the University of British Columbia, Okanagan campus, set out to answer this question. The study, published in April of 2020, looked at regular cannabis users in comparison to non-users to determine if they showed differences in pain sensitivity.
According to St. Pierre, both opioids and cannabis have been “associated with increases in pain sensitivity following acute use,” so the researchers hypothesized that cannabis would produce similar hyperalgesia to opioids. St. Pierre’s co-author, Zach Walsh, who heads the UBC Therapeutic Recreational and Problematic Substance Use Lab that hosted the study, told Science Daily he was relieved to find that frequent cannabis use did not increase pain sensitivity: “This study should come as good news to patients who are already using cannabis to treat pain. Increases in pain sensitivity with opioids can really complicate an already tough situation.”
The researchers studied 83 adult students from UBC, divided into regular cannabis users (more than 3 times per week) and non-users (either never used cannabis, or hadn’t used within the last month.) The users were recreational users and did not hold medical marijuana cards. They assessed pain sensitivity with the cold-pressor task, a common way of assessing cardiovascular function, pain sensitivity and tolerance in clinical trials. In the cold-pressor test, participants submerge one hand in ice water for up to two minutes and “pain of minor to moderate intensity builds until the individual withdraws their limb from ice water.” The researchers assessed pain with a Visual Analogue Scale, which is a “validated subjective measure for acute and chronic pain.” Pain sensitivity was defined as the first time participants reported pain (in seconds), while pain tolerance was defined as the total length of time that participants kept their hands submerged in ice water. The participants were instructed to keep their hand submerged until they could not stand it anymore.
The results indicate that there is no difference in pain sensitivity and tolerance between young, healthy cannabis users and non-users. This finding is in stark contrast to opioid therapy, and, according to the researchers, is an important distinction that health care providers (cannabis doctors especially) should consider when choosing between different therapies for pain management. In short, “cannabis may not carry the same risk of hyperalgesia as opioids.” While these results are encouraging, there are some important limitations that must be kept in mind.
Cannabis use was self-reported and the researchers did not confirm cannabinoid metabolites, so the researchers admit that some participants could have been assigned to the wrong group. How long people had used cannabis prior to the test was also not collected, so perhaps the participants had not used cannabis for long enough to alter pain reactivity. Additionally, the cold-pressor task may not mimic pain as experienced in real life. And lastly, the participants were healthy young adults, so the results may not be generalized to the wider population, or even patients who are using cannabis to manage chronic pain.
In the conclusion of their paper, the researchers call for ecological momentary assessment (EMA) studies to better understand how cannabis interacts with pain in real life. EMA studies allow research participants “to report on symptoms, affect and behavior close in time” to an experience, and they typically sample many events and time periods, thus providing a more detailed measurement of mood and behavior than other research methods. Digital technologies like Jointly allow people to assess their pain, relief and cannabis use in real time.
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