The evidence on medical cannabis
A promising black box
Cannabis is quickly gaining momentum as a wellness trend with people touting its many medicinal properties. But is there enough data to support the hype?
Dr. Dwight Moulin, Scientist at Lawson, Professor at Western University and the Earl Russel Chair of the Western Pain Program, is a leading expert in the area of pain management. He answers some common questions to shine a light on the evidence for medical cannabis.
What are cannabinoids and how are they being used?
There are hundreds of different chemicals in the cannabis flower, yet only a few have ever been studied. The most well-known is delta-9-tetrahydrocannabinol (THC), the main psychoactive compound. Cannabidiol (CBD) is another major constituent of the plant. Both act on cannabinoid receptors in the body.
THC is considered a painkiller. It’s analgesic mechanism of action is similar to opioids, but THC can offer relief without side effects like constipation and respiratory depression. CBD has a completely different way of producing effects in the body.
What evidence do we have?
We have many trials testing THC for pain relief, especially for people with nerve or neuropathic pain. CBD may be analgesic as well, but we don’t have any published clinical trials of CBD use in humans for pain relief. We have very compelling testimonials suggesting benefit and some studies are underway. It’s a huge gap.
Why do we not have more randomized controlled trials?
Trials using THC are often of short duration with small numbers of participants. Even when the attempt is made for a double blind study, the euphoria and drowsiness from THC makes blinding difficult – the participants tend to know if they’ve taken THC and it can alter the data.
Medical cannabis use has focused almost entirely on THC for the last five to 10 years, but more attention is being given to CBD. People started noticing strains high in CBD were helping them with pain or other conditions, and the anecdotes are now overwhelming.
Because these are natural products, there are fewer incentives for industry to pay for the trials and patent a formulation. Researchers have to look elsewhere for funding.
Are we aware of risks related to cannabis use?
We believe that smoked cannabis carries increased risk to the lungs; although, short term studies have not shown adverse effects. While we don’t recommend smoking cannabis, smokers can reduce the risks to the lungs by vaporizing at lower temperatures or they can switch to ingested oils, edibles and capsules.
About 10 per cent of people who use cannabis are at risk of developing an abuse disorder. The greater the feeling of euphoria the drug provides, the more likely a person gets addicted. The risk of addiction with nicotine is much higher at 50 to 60 per cent.
When THC is used under the age of 25 by predisposed individuals it can increase the risk of psychosis. That’s something we are quite concerned about. Psychiatrists are seeing more and more psychosis, including schizophrenia, in individuals who used cannabis at younger ages, and we are seeing the same through many observational studies.
Do we know enough about the health benefits and potential harm?
An exciting potential benefit is that cannabis may be used as an opioid-sparing technique. That is, it can be used in place of opioids to relieve pain. It has fewer side effects than opioids and is handled well by most people. Cannabis has no risk of respiratory depression – no one’s ever died from an overdose. Across the border in states where recreational cannabis has been legal for many years, they’ve seen the incidence of opioid-related deaths going down. The trade-off is that there is a modest increase in impaired driving.
Overall, we are confident that medical cannabis can be prescribed safely and despite some of the limitations, we have reasonable evidence for THC as a painkiller. We don’t know enough about CBD yet because we don’t have the data.
What are some of the most common uses right now?
The most common use is pain management, for both acute and chronic pain such as arthritis, nerve pain, headaches and migraines. Cannabis may also be beneficial for people with inflammatory bowel disease. CBD is being used for some forms of intractable epilepsy and a major area of focus is using CBD for relieving symptoms of post-traumatic stress disorder (PTSD) and anxiety, as well as for athletes with post-concussion syndrome.
What are the next steps?
We have very compelling testimonials suggesting benefit and some studies are underway. Right now scientific evidence on CBD is almost a black box.
We are still investigating dosing of medical cannabis and how much CBD to give with THC. Right now we use low amounts and go from there to see how each individual reacts. The real limitation is that cannabis is expensive and some people don’t get the full benefit because they can’t afford it.
We don’t want people smoking it and ingested cannabis can take one or two hours to kick in, making accidental overdoses more likely. Administering it under the tongue is being explored, which could be a great option because it bypasses the liver and goes directly to the arteries, brain and spinal cord.
We need short-term randomized controlled clinical trials that are blinded, along with long-term pragmatic studies to look at the efficacy and safety over time. I do expect some clinical trials on CBD to come out soon but it will probably be a few years before we have solid information. Right now CBD is almost a black box, and we are relying on testimonials.