What Pain Specialists Need to Know About Medicinal Cannabis
An interview with Barth Wilsey, MD
A growing number of states have approved medical marijuana (cannabis) to treat a variety of conditions, including neuropathic pain, spasticity, and pediatric epilepsy. Despite the increasing popularity of these treatments, there’s been an absence of uniform standards and guidelines in place to help medical professionals navigate the rapidly changing landscape in the most effective way. As a result, many pain specialists are left grappling with a host of important issues when it comes to incorporating cannabis into a broader pain treatment strategy. Here is some insight from an experienced practitioner on treating pain with cannabis.
Q How did you get interested in studying medicinal cannabis?
Dr. Wilsey: In 1994, I was a pain research fellow at University of California, San Francisco (UCSF). As part of my duties, I worked in the UCSF Pain Clinic and wrote many prescriptions for chronic pain patients. Several patients informed me that prescription medications were ineffective and they preferred to use cannabis. They obtained the cannabis from cooperatives in Oakland, California.
This was 2 years prior to the passage of Proposition 215, the Compassionate Use Act of 1996.1 Several years later, after the California Legislature passed the Medical Marijuana Research Act of 1999,2 the UC Center for Medicinal Cannabis (CMCR) was established.3 With the CMCR’s assistance, I was able to obtain the requisite federal approvals from the Department of Health and Human Services (DHHS), Drug Enforcement Administration (DEA), Food and Drug Administration (FDA), and National Institute of Drug Abuse (NIDA). Subsequently, we performed 2 randomized, controlled crossover studies demonstrating the efficacy of medicinal cannabis in the treatment of neuropathic pain.4,5
Q How can pain specialists understand some of the issues regarding medical cannabis?
Dr. Wilsey: My CMCR colleagues and I decided to use our collective experience studying cannabis to provide some guidance on this issue to other physicians.6 We borrowed concepts developed for the prescription of opioids—namely, the use of a written agreement to describe and minimize risks when discussing medicinal cannabis with patients. Intended to be printed and distributed to patients, this agreement was developed for patients to read at home, so they could get a clear understanding of the benefits and risks involved and query providers at subsequent visits if they have questions.
Q Are most patients appropriate candidates for medicinal cannabis? And if not, can you explain what groups might not be a good fit for using this treatment?
Dr. Wilsey: When recommending cannabis to patients, pain specialists must recognize that some people will have an increased risk from harmful effects. Contraindications include pregnant women, individuals with coronary heart disease, and/or those with serious mental illness (eg, schizophrenia and bipolar disorder).
Q What advice do you offer for pain specialists to guide patients in getting the therapeutic benefits for neuropathic pain from medicinal cannabis with minimal side effects?
Dr. Wilsey: Pain physicians should recommend that patients use the lowest dose of delta-9-tetrahydrocannabinol (THC) that the patient finds to be effective. This is important not just to minimize the psychoactivity, but also to decrease cognitive impairment. We performed human laboratory experiments where participants received pain relief with only 1.3% delta-9-THC.5 There was very little of either psychoactivity or cognitive impairment at this dose level.
However, longer-term studies (weeks to months) are needed before we can conclude anything definitive concerning whether or not a dose this low would be effective over a long-term period. Yet it still makes sense to recommend that patients use the lowest dose available that provides pain relief so that side effects are minimized.
There is also a growing interest in using medicinal cannabis that contains cannabidiol (CBD) in addition to delta-9-THC. CBD can counteract some of the negative effects of delta-9-THC, such as psychoactivity, although such findings have not always been consistent. I expect that we will see more investigative work on the combination of these two cannabinoids in the future (See related article).
Q What should pain specialists know about any potential dangers to the lungs when people smoke cannabis?
Dr. Wilsey: Cannabis increases cough, sputum production, hyperinflation, and upper lobe emphysematous changes.7,8 Although regular cannabis smoking leads to bronchial epithelial ciliary loss and impairs the microbicidal function of alveolar macrophages, evidence is inconclusive regarding possible associated risks for lower respiratory tract infection.9
We also know that cannabis smoke contains carcinogens, but in several well-respected epidemiological studies, light or moderate use of cannabis did not seem to increase the risk of lung cancer or cancer of the upper airways. However, one study found that heavy use (defined as more than 50 times of use during the lifetime) doubled the risk of developing lung cancer over a 40-year timeframe.10 This is certainly important to keep in mind.