Feeling your pain

Long-term cannabis use, unlike opioids, doesn’t effect patients’ pain tolerance, new research suggests


Michelle St. Pierre had just had dental surgery, and she was curious how cannabis would work as an alternative to opioid painkillers. As a Ph.D. candidate studying clinical psychology at the University of British Columbia, Okanagan, St. Pierre was familiar with cannabis’ pain-alleviating qualities. After all, her area of focus is mental health and pain, and the lab she works in regularly experiments with cannabis, psychedelics and human behavior. 

However, when St. Pierre used cannabis after her surgery, when she was experiencing acute pain in her gums, she felt like her pain actually intensified. She could feel the blood rushing through her body, and pulsating in her jaw, and couldn’t focus on anything except her mouth ache.

“I was wondering what’s going on? Is this just all in my head? Is there research on this?” St. Pierre recalls. So, like any good scientist she hit the books. “I went through the literature and sure enough I found that in experimental settings, in a laboratory when people got high, it shows that there’s this increase in pain sensitivity.”

St. Pierre had heard of a similar side effect of long-term opioid usage, known as hyperalgesia. Between her own personal experience and the literature, she had a suspicion there might be a similar effect with long-term cannabis use. 

So, she designed a laboratory test to see whether or not long-term cannabis use affected one’s sensitivity to pain. And St. Pierre did not find what she expected. 

“Opioid-induced hyperalgesia is actually a really fascinating phenomenon,” she says. Some patients using opioids long-term to manage chronic pain actually increase their sensitivity to acute pain in the process. This presents a challenging problem for doctors and pharmacists trying to prescribe painkillers to patients with ongoing, persistent pain.

“Interestingly, there’s also been studies where, before a surgery they’ll give half the subjects morphine and then the other half won’t get anything,” says St. Pierre. Following the surgery, doctors monitored how much pain medication the two groups were requesting — and the group who got morphine prior to the surgery, actually demanded more pain medication than the control group, St. Pierre says.  

“So the researchers deduced that they had created this increased-sensitivity-to-pain state in the body in an acute time frame,” she says. 

Which sounds paradoxical, but could explain the loss of opioid efficacy in some patients, according to a study published in Pain Physician

But does this same phenomenon occur in long-term cannabis patients? 

To answer that question, St. Pierre designed an experiment to test pain tolerance in long-term cannabis users and people who had never used cannabis at all. In order to ensure accuracy, the cannabis users involved in the study had to use cannabis at least three times a week, but couldn’t be high at the time of the test. Otherwise their high might skew the results, according to St. Pierre. 

Then, both groups had to feel the pain. 

“Inducing pain in the lab is actually really difficult because a lot of what makes pain so unbearable is that we can’t control it: it’s unexpected; it might even scare us a little bit,” St. Pierre explains. “And when we induce pain in the lab, we sort of eliminate that whole component. So, we do the best that we can to try and have stimuli that still activate the pain sensors inside the body in the same ways that would occur in nature.”

They achieved that with a “cold pressor bath” — what St. Pierre called a “glorified ice bucket.”

Subjects were asked to submerge their hand and forearm in the cold pressor for as long as they could manage and they were tested on three different aspects of pain: Sensitivity, measured by when subjects first experienced pain; tolerance, measured by how long they could withstand it; and intensity, measured by asking them afterwards how bad the pain was on a scale of 1-10. 

St. Pierre expected to see what would have been called “cannabis-induced hyperalgesia.” However, her results didn’t support that. 

“We found that there was no difference in pain tolerance when we compared [regular, long-term cannabis users] to people who hadn’t used cannabis ever,” she says, clearly excited. “When you’re comparing negative side effects of opioids to those of cannabis, here cannabis is again coming out on top.”

That opens the doors for a lot of other research. It begs questions like, psychologically, what is the difference between chronic pain and acute pain? Why do cannabis and opioids only seem to treat chronic pain? And what about THC makes it such a reliable and generally safe painkiller? 

“From a scientific perspective this is really exciting,” St. Pierre says. “It really opens up a bunch of new questions in the pain research world and in the cannabis research world.”