Laird Harrison

May 26, 2015

PALM SPRINGS, California — Physicians must become better prepared to answer patients' questions about cannabis because its use in medicine is exploding, according to a leading researcher.

"It's high time we got up to speed with the language and the issues around communication on this," said Mark Ware, MBBS, MSc, from McGill University Health Centre in Montreal, Quebec, Canada.

Dr Ware has researched the use of cannabis in pain control and gave an overview of the field in a plenary talk here at the American Pain Society (APS) 34th Annual Scientific Meeting.

Researchers are beginning to separate the analgesic constituents of cannabis from the psychoactive ones, he said. "But in the meantime, many jurisdictions have legalized cannabis for medical use, and more and more patients are using it to treat their pain. Physicians must be prepared to counsel them on potential risks and benefits."

If doctors brush off these patients, he warned, "they'll leave the clinic and go to one of those people who are selling licenses down the road for $400. They'll get their card. And there's no follow-up and no monitoring and no chance to really learn as physicians and no chance for us to help guide them in that pathway."

Dr Ware gave the example of two patients who visited him in his pain clinic in one day. The first was a 62-year-old woman who had experienced radiation-induced neuropathic pain in her chest for 5 years after a double mastectomy. Conventional pain relievers had not helped. She had never smoked marijuana before, but now she wanted to know if she should try it.

The other patient was 42 years old, overweight, inactive, and recently diagnosed with rheumatoid arthritis. She had experienced diffuse body pain for 20 years and had been smoking 3 g of marijuana per day for most of that time. She wanted to know if Dr Ware would authorize this use as a medical treatment.

Answering such questions is not easy, Dr Ware said. To help, physicians must come up to speed not only with the research but with the way marijuana is packaged, sold, and used on the street.

"Learning how to speak 'cannabis' is not always easy," he said. "You have to learn about weed and pot and joints and blunts, dabs, and doobs."

He also advised clinicians that many patients feel stigmatized and nervous about discussing their marijuana use — not least because of the strong smell from smoking it. "Quite frankly it stinks," he said.

Recent research promises to reduce the stigma as well as side effects, he said. "Cannabis is where opioids were 20 to 30 years ago."

Researchers have progressed from isolating the active compounds in the plant to identifying cannabinoid receptors and recognizing an endogenous cannabinoid system, he said. "This is a very valid target for therapeutics."

Already this work has identified over 100 cannabinoids. Two of the best understood are tetrahydrocannabinol (THC), the ingredient for which marijuana plants have been bred for recreational use, and cannabidiol (CBD), which takes the place of THC in hemp used for fiber.

Some studies suggest that cannabinoids act as synaptic circuit breakers. "They can presumably put the brake on nerves that are firing abnormally," said Dr Ware.

In this way, they have shown promise in the treatment of chronic constriction injury, sciatic nerve ligation, spinal cord injury, multiple sclerosis, cancer pain, osteoarthritis, visceral pain, muscle pain, inflammatory nociceptive pain, brachial plexus avulsion, trigeminal neuralgia, and neuropathy caused by HIV infection, said Dr Ware.

In addition to herbal marijuana, prescription cannabinoids already include the following:

  • Dronabinol, an oral capsule for chemotherapy-induced nausea and vomiting and for anorexia associated with HIV;

  • Nabilone, an oral capsule for chemotherapy-induced nausea and vomiting; and

  • Nabiximols, an oromucosal spray for multiple sclerosis–associated neuropathic pain, spasticity, and advanced cancer pain.

Cannabinoids might even help with some public health problems. One study (JAMA Intern Med. 2014;174:1668-1673) showed that states with laws legalizing medical marijuana had lower rates of mortality from opioid analgesics.

But they do come with risks. Short term, these are familiar: memory loss, impaired motor coordination, altered judgment and — in higher doses — paranoia and psychosis.

The longer-term adverse effects include symptoms of chronic bronchitis and increased risk for chronic psychosis in people with a predisposition to such disorders.

They also appear to alter brain development in children, affecting educational outcomes, lowering intelligence quotient, and diminishing life satisfaction and achievement.

"Alongside the fact that we're looking at cannabis to use as therapy, we have be very careful we don't spill that message over and tell kids that it's okay to use when they're very young," said Dr Ware.

Cannabinoids are contraindicated in psychosis, unstable heart disease, and pregnancy, he said. And clinicians should watch out for patients with a history of legal issues or criminal charges.

It's important to try to validate that the patient's interest in the drug is for truly medical use, he added. In the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders, the American Psychiatric Association describes a "cannabis use disorder" in terms similar to those used for the abuse of opioids, said Dr Ware.

Patients inclined to abuse might insist on a medical document for dried cannabis rather than trying other treatments. They might use the drug frequently, have trouble stopping, and be addicted to other substances. Friends or family might be concerned about their use, and it may affect their schooling, work, or social functioning.

"Use the opportunity when a patient is asking you about cannabis," said Dr Ware. "Is she someone with cannabis disorder presenting as someone who is using it therapeutically?"

To understand better what patients might be helped, the province of Quebec, Canada, has launched a registry collecting data on patients who are prescribed marijuana, Dr Ware said.

And he is watching with interest how different states in the United States and nations around the world experiment with a variety of legal approaches.

"We're at a very interesting time," he concluded.

The APS has been working on a white paper to outline its position on cannabinoids, the society's president, Gregory W. Terman, MD, PhD, told Medscape Medical News.

"I think people are opening their eyes to the possibilities," he said.

Dr Ware's talk illustrated the potential for using targets in the endo-cannabinoid system, he said. "I think most people agree that marijuana is not the way to go, and there may be cannabinoids that are more specific on pain with less effect on mental status."

Dr Ware disclosed a research grant to his institution from CanniMed. Dr Terman has disclosed no relevant financial relationships.

American Pain Society (APS) 34th Annual Scientific Meeting. Presented May 16, 2015.


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