Tuesday August 31 2010
This trial was too small to know if the results were due to chance
“Smoking cannabis from a pipe can significantly reduce chronic pain in patients with damaged nerves,” reported the BBC. It added that improvements in sleep and anxiety were seen.
This news story is based on a small randomised controlled trial in 23 people, which found that a low dose of inhaled cannabis (lower than that needed to cause euphoria or a “high”) modestly improved reported pain in patients who had neuropathic pain.
This is a well-conducted study, but its small size means that it is not possible to tell whether the results demonstrate a real association between cannabis and pain relief, or if they are due to chance.
More research in larger groups of people over a longer period of time is needed to see if the effects of cannabis for this type of pain can be replicated. In addition, there are health concerns related to the use of smoked cannabis, including mental health problems and lung damage.
It is important to point out that cannabis is a class B drug, which is illegal to possess or supply, and is not licensed in any form for medical use.
Where did the story come from?
The study was carried out by researchers from McGill University, Canada, and was funded by The Canadian Institutes of Health. The study was published in the (peer-reviewed) Canadian Medical Association Journal.
This research was covered well by The Daily Telegraph and the BBC, though the study did not find any evidence for effects on anxiety or depression, as the Telegraph headline suggests.
What kind of research was this?
This randomised controlled trial investigated whether cannabis can relieve neuropathic pain (neuralgia) – severe pain caused by the abnormal activity of nerve cells. Various events can set off neuropathic pain, including surgery, trauma or shingles.
The researchers say that although there are drug treatments for neuropathic pain, such as anticonvulsants, antidepressants, opioids and local anaesthetics, their effectiveness varies between patients. Some patients are put off taking them because of unpleasant side effects. They say there is anecdotal evidence that cannabis relieves chronic neuropathic pain and improves sleep. The researchers wanted to investigate whether these reported effects could be replicated under controlled experimental conditions.
This type of study design is the most appropriate way of determining whether a drug is effective. However, this was a very small trial in only 23 people, so it is not possible to conclude that the results are due to chance alone.
What did the research involve?
The study recruited people who had experienced neuropathic pain for at least three months as a result of trauma or surgery. The participants ranked their current level of pain on a 10-point scale, and patients reporting pain intensity greater than four were included. Excluded from the study was anyone whose pain was due to cancer, anyone who had heart or lung disease, and those who had any type of substance abuse, a history of psychiatric disorders, or who were pregnant. In total, 23 people were eligible to participate in the study.
The effect of smoking cannabis with the active ingredient tetrahydrocannabinol (THC) was compared to smoking cannabis in which the THC had been removed (the control). Different potencies of THC were also compared to each other. Participants were not told which treatment they were given.
The control cannabis that had the THC removed was provided to the researchers by the US National Institute of Drug Abuse. The cannabis doses were prepared by blending the flowers and leaves of the plant to make three different potencies of the active drug (2.5%, 6.0% and 9.4% of THC).
Cannabis doses were delivered as single smoked inhalations taken through a pipe. The participants were instructed to inhale for five seconds as the cannabis was lit, hold the smoke in their lungs for 10 seconds, then exhale. The patients were observed taking the first dose. They then took subsequent doses at home, three times daily for five days. After 14 days, the participants swapped treatments so that those who had received the cannabis without THC then received cannabis containing the active drug. And those who had received active cannabis then received the placebo or a different dose of cannabis treatment.
In total, participants had four cycles of treatment where they received doses of 0%, 2.5%, 6% and 9.4% THC. Throughout the trial, the participants continued any routine medications that they were taking.
On the first day of each treatment period, the participants were asked about their feelings of pain, and how relaxed, stressed or happy they were. Their heart rate was also measured and a blood sample taken. During the five days of treatment or placebo, the participants were contacted by telephone and asked about their pain, how they were sleeping, their medication, and whether they were having any side effects. A urine sample was taken every day. On the fifth day of each treatment, a blood sample was taken and the participants were asked more questions about their pain, mood and quality of life.
What were the basic results?
The study had screened 113 participants but only 23 were eligible. Out of these, 21 completed all four cycles.
The researchers found that the average pain intensity was significantly lower on 9.4% THC cannabis (score 5.4 out of 10) than on 0% THC cannabis (6.1 out of 10) (p=0.023). However, no other comparisons between the different doses were found to be statistically significant.
Participants using 9.4% THC cannabis reported finding it easier to fall asleep and had better quality of sleep than those taking 0% THC. No differences in mood or quality of life were seen with the different THC potencies.
Of the reported side effects, none were serious or unexpected. The most frequent side effects reported by participants when taking 9.4% THC cannabis were headache, dry eyes, burning sensation, dizziness, numbness and cough. Feeling “high” and euphoric was reported once in the 2.5%, 6% and 9.4% THC cannabis treatment periods.
How did the researchers interpret the results?
The researchers said that the 25mg herbal cannabis with 9.4% THC, administered as a single smoked inhalation three times a day for five days, significantly reduced average pain intensity compared to placebo in adults with chronic post-traumatic or post-surgical neuropathic pain. They also said that there were improvements in measures of sleep quality, but that long-term safety and efficacy studies are needed.
This placebo-controlled trial found that cannabis containing 9.4% THC could reduce neuropathic pain compared to the placebo. However, this was a small trial with only 23 participants, so it is difficult to tell whether these results demonstrate a real association, or if they are due to chance. A much larger trial would be needed for a longer period to assess the long-term outcomes of such a treatment. Additionally, there are health concerns related to the use of smoked cannabis, including mental health problems and lung damage. Further research is needed to assess such potential side effects over the long term.
The researchers say that their study provides a way of looking at the short-term effects of smoked cannabis in a placebo-controlled trial. It is important to point out that cannabis is a class B drug, which is illegal to possess or supply, and is not licensed in any form for medical use.