Cannabis to Treat Chronic Pain?

Though marijuana remains a Schedule I controlled substance under federal law, 23 states and the District of Columbia have passed their own laws allowing for the medical use of cannabis. In both Canada and Israel, certain physicians are licensed to prescribe cannabinoid drugs for specific conditions; other countries, like Germany, are working to determine regulatory frameworks to follow suite.

With medical marijuana becoming an option for an increasing number of people, physicians are likely to face questions from patients about cannabis - or treat patients already self-medicating with the drug.

At the American College of Rheumatology winter symposium in Snowmass, Colorado in January, University of Michigan rheumatologist Daniel Clauw, M.D., presented the potential benefits and risks of using cannabinoids to treat chronic pain. Data is lacking on cannabinoid treatment for many chronic conditions, he reported, but given large numbers of long-term recreational users, the "worst case" risks are probably well-known.

There are more than 80 cannabinoids in plant-derived cannabis, but the two of most interest to doctors are THC (tetrahydrocannabinol), which binds both to CB1 cannabinoid receptors in the brain and CB2 receptors in the immune and peripheral nervous systems, and CBD (cannabidiol) an antagonist of chemicals that bind to CB receptors in the brain and body. CBD does not have psychoactive effects, but has been shown in animals to have anticonvulsant effects. It may also have anti-inflammatory and analgesic properties.

Rheumatology Network caught up with Dr. Clauw to discuss the potential risks and benefits of cannabinoids and how they compare with pharmaceuticals currently used to treat chronic pain.[[{"type":"media","view_mode":"media_crop","fid":"46000","attributes":{"alt":"Daniel Clauw, M.D.","class":"media-image media-image-right","id":"media_crop_329240909777","media_crop_h":"0","media_crop_image_style":"-1","media_crop_instance":"5299","media_crop_rotate":"0","media_crop_scale_h":"0","media_crop_scale_w":"0","media_crop_w":"0","media_crop_x":"0","media_crop_y":"0","style":"font-size: 13.008px; line-height: 1.538em; float: right;","title":"Daniel Clauw, M.D.","typeof":"foaf:Image"}}]]

Why is it important for rheumatologists to know about the data on cannabinoids?  Are there particular rheumatic conditions where cannabinoids have promise?  

There are two separate effects of cannabinoids. In the brain, they bind to receptors that generally decrease pain. In the peripheral tissues, they have anti-inflammatory effects. So they may be helpful for conditions such as fibromyalgia because of the central nervous system analgesic effects, as well as in autoimmune diseases for their anti-inflammatory effects. 

How does cannabis work to relieve pain, and why does the type of pain matter?  

Most classic rheumatic disorders have a component of auto-immunity, and specific cannabinoid compounds that work primarily in the periphery and primarily on immune effects might be helpful in those diseases. On the other hand, in conditions such as fibromyalgia that are primarily due to central nervous system pain amplification, other cannabinoids might be helpful because of their central nervous system analgesic effects.

Does the type of cannabinoid and method of delivery seem to make a difference in its efficacy and safety? 

For chronic pain it is generally much better to take a drug orally than smoke it, because when you smoke a drug the level goes up very quickly and makes it more likely to get high.  So individuals using cannabis as their cannabinoid (in the U.S., this is the most practical manner to get access to a cannabinoid for pain) they should try to use foods and teas made from cannabis to control their pain.  

In your talk, you mentioned that cannabinoids have an anti-inflammatory role, but you also report that cannabinoids aren't recommended for peripheral pain. Why is that?   

So far, there is no evidence that cannabinoids are helpful for classic rheumatic diseases such as rheumatoid arthritis, lupus, or osteoarthritis. Those studies are ongoing. There is evidence that cannabinoids can be effective in fibromyalgia, and in general the best evidence for cannabinoids is in individuals with pain that is more of central nervous system origin.   

What are the main risks of treating chronic pain with cannabinoids? 

They have side effects just like any other class of drug. But when individuals use cannabinoids for pain and especially when they are taking oral formulations, they have far fewer side effects of cannabinoids than people generally associate with smoking marijuana for recreational use. Cannabinoids taken orally (i.e marijuana baked into foods or made into teas) are generally well tolerated compared to other classes of drugs we use to treat chronic pain. 

How do the risks compare with the risks of other drugs used to treat long-term pain? The best comparison I can make is to opioids. For most individuals with chronic pain, the risk of trying a cannabinoid is far, far less than the risk of taking an opioid.  Twenty-five thousand people in the U.S. die each year from opioid overdose, two-thirds of which is from prescription opioids. Cannabinoids cannot directly cause death like opioids.    

References:

Jones NA, Hill AJ, Smith I, et al. Cannabidiol Displays Antiepileptiform and Antiseizure Properties In Vitro and In Vivo. Journal of Pharmacology and Experimental Therapeutics 2009;332(2):569–577.  doi: 10.1124/jpet.109.159145.

Ablin J, Ste-Marie PA, Schäfer M, Häuser W, Fitzcharles M-A. Medical use of cannabis products. Der Schmerz Schmerz 2016;30(1):3–13. Epub ahead of print.