Taking a marijuana pill is more effective at relieving pain than smoking the drug, a new US study of daily marijuana smokers has shown, but the authors warn the findings may not translate to non-regular users.
Medical marijuana is already allowed in at least 18 US states and in Canada but remains illegal in Australia.
The new study, conducted by the College of Physicians and Surgeons at Columbia University and published in the journal Neuropsychopharmacology, involved 15 males and 15 females who smoked marijuana every day.
Subjects either took a placebo, smoked marijuana, or took dronabinol, a pill containing the psychoactive ingredient in marijuana. The researchers ensured the participants had not smoked in the hours before the tests began and were not using other drugs or alcohol.
Pain tolerance and duration were tested using the Cold-Pressor Test, in which test subjects put their left hand into ice water. The researchers timed how long the participants could hold their hand in the water before it became painful and how long they could withstand the pain before removing their hand. Cardiovascular effects were also measured.
“Dronabinol administration decreased pain sensitivity and increased pain tolerance that peaked later and lasted longer relative to smoked marijuana,” the researchers wrote.
However, the authors urged caution in applying their results to the general population.
“A primary caveat of the current findings is that the study population consisted of daily marijuana smokers; this study limitation should be considered when interpreting the findings and placing them within the context of the potential therapeutic feasibility of cannabinoids,” the researchers wrote.
Professor Jake Najman, Director of the Queensland Alcohol and Drug Research and Education Centre at the University of Queensland said the new research “increases the pressure on Australian governments to consider relevant legislative initiatives.”
“Present prescribing for pain relief frequently involves the use of opioid. There is a need to consider whether marijuana may be a safer alternative,” he said.
However, Dr Michael Vagg, Clinical Senior Lecturer at Deakin University School of Medicine and Pain Specialist at Barwon Health, said the results were very preliminary and “nothing to be too excited about.”
“Dronabinol is known to be effective in some types of chronic pain, but finding a cannabinoid drug that doesn’t cause an unacceptable number of psychotic symptoms is where the field has been stuck,” he said.
“It’s important that the participants in the study were all regular recreational users, and therefore would tolerate the dronabinol well. This hasn’t tended to be the case when used in clinical trials on real patients,” said Dr Vagg.
“It’s a useful proof of concept study but we are still a long way from having a cannabinoid analgesic drug that is both effective and safe enough for routine use.”
Dr Alex Wodak, Emeritus Consultant, Alcohol and Drug Service at St Vincent’s Hospital and a Visiting Fellow at the University of NSW’s Kirby Institute also urged caution in interpreting the results.
“Dronabinol is poorly and erratically absorbed when swallowed, so the blood levels are unpredictable. This limits its clinical usefulness,” he said.
Dr Wodak said the side effects of recreational cannabis are modest and when cannabis is provided under medical supervision are likely to be even smaller.
“The health risks associated with extended release prescription opioids, the most commonly prescribed drugs used to manage chronic pain, are considerable and far greater than medicinal cannabis. Where is the evidence that intoxication or abuse is a problem when cannabis is used medicinally? And if so, how does this compare to the benefits?” he said.
Dr Wodak said dronabinol has been available in some countries for some years but it has attracted little interest compared to the use of plant cannabis or the mouth spray nabiximols.