For Pain Relief, Cannabis May Be No Better Than a Placebo

Previous research has shown the placebo effect can be extremely powerful, rivaling ibuprofen or morphine

Bags of Marijuana with "For Medical Use Only" written on them
Thirty-seven U.S. states and D.C. have laws permitting the use of medical marijuana. Justin Sullivan via Getty Images

Cannabis has been used around the world for years to reduce pain. In some U.S. states, patients can use medical marijuana to treat conditions such as multiple sclerosis, chronic pain and depression. But a new analysis suggests that cannabis’ pain-relieving effect may stem at least partially from a belief that it will work. 

In a study published in the Journal of the American Medical Association, researchers analyzed the results of 20 double-blind, placebo-controlled trials testing both synthetic and natural cannabinoids. The trials included 1,459 participants between the ages of 33 and 62 with neuropathic pain, multiple sclerosis or other pain. 

Participants who received a cannabis placebo tended to report a significant reduction in pain, despite not having used the drug, the researchers revealed. In fact, regardless of whether patients used the active treatment or the placebo, they reported similar levels of pain relief.

“The placebo response amounted to 67 percent of the pain relief associated with genuine cannabinoids,” lead author Karin Jensen, a senior researcher in the pain neuroimaging lab at the Karolinska Institutet in Sweden, tells CNN’s Sandee LaMotte. 

Previous research has shown that the placebo effect can be extremely powerful, rivaling common pain-relieving drugs, such as ibuprofen, or even morphine, Kathryn T. Hall, a placebo researcher at Harvard medical school, told the Guardian’s Zoë Corbyn in October. 

“The response is strongest in more neurological and psychological conditions; placebo effects appear to have little impact on the outcome of clinical trials to treat cancer, viruses or bacterial infections,” she told the publication. “Other conditions with high placebo responses in clinical trials include depression, irritable bowel syndrome [IBS], epilepsy, hypertension and asthma. And not everyone responds equally.” 

The placebo effect doesn’t mean a drug is ineffective, but rather, it can mimic the medication’s effect through different neurobiological pathways, Ted J. Kaptchuk, director of Harvard Medical School’s Program in Placebo Studies and the Therapeutic Encounter, says in a statement

“It’s an interesting and very real phenomenon,” Harriet de Wit, an experimental psychologist at the University of Chicago who was not involved in the new study, tells CNN. “It’s certainly not ‘all in your head.’ And yet, there are some brain circuits that are involved in creating those thoughts and those expectations.”

In cannabis studies where patients were poorly blinded—meaning they were able to tell which treatment they received—the placebo effect was lower, the researchers found. 

The team also measured how cannabis studies were covered in the media to see how that may have contributed to the therapeutic effects reported by patients. The team examined 136 news items in media and blogs and categorized each story as positively, negatively or neutrally characterizing cannabis as an effective treatment for pain relief. They found that regardless of a study’s outcome, an “overwhelming majority” of media coverage tended to report that cannabis had a positive effect, writes co-author Filip Gedin of the Karolinska Institutet for the Conversation.

While the researchers could not prove that news coverage contributed to the placebo effect, the results show that scientists need to be “extra rigorous” in their clinical trials of treatments that get a lot of media attention, Gedin writes. 

So, for those with chronic pain, choosing whether to use cannabis might be more complicated than previously thought.

“By the strict orthodoxy of modern medicine, a doctor would say cannabis products don’t work—they’re no better than a placebo,”  Kaptchuk says in the statement.

But chronic pain is known for being difficult to treat, and clinical trials aren’t the same as real life, per the statement. After checking with a doctor, “if something helps relieve your pain and doesn’t cause any significant harm, I would say go ahead and use it,” Kaptchuk says in the statement.