Cannabis for chronic pain: Not a simple solution

CHRONIC PAIN IS COMPLICATED

Peripheral neuropathy, by definition, is a chronic pain condition. Unlike acute pain, chronic pain is characterized by biologic, psychologic, and social complexities that require nuance to manage and study.

Such nuance is lacking in most recent reviews of the medical use of cannabis. The conditions in question are often studied as if they were transient and acute, eg, employing shortterm studies and rudimentary measures such as numeric pain-rating scales or other snapshots of pain intensity. Results of these shortsighted assessments are impossible to extrapolate to long-term outcomes.

Whether cannabis therapy for chronic pain conditions is sustainable remains to be seen. Outcomes in chronic pain should not be defined simply by pain reduction, but by other dimensions such as changes in pain-related disability and quality of life, development of pharmacologic tolerance or dependence, adverse effects, and other “collateral damage.” We are far from understanding these issues, which require highly controlled and regulated longitudinal studies.

A recent Cochrane review³ of the efficacy of cannabis-based medicines for chronic neuropathic pain found that harms might outweigh the benefits. The quality of evidence was rated as very low to moderate; the reviewers cited small sample sizes and exclusion of important subgroups of patients (eg, those with substance abuse or other psychiatric comorbidities). Such exclusions are the crux of a major problem with cannabis research: studies are not naturalistic. The gritty reality of chronic pain management is paramount, and failing to consider the high-risk biopsychosocial factors typical of patients with chronic pain is naïve and, frankly, dangerous.

COGNITIVE AND MOTIVATIONAL PROBLEMS

The true danger of cannabis lies in what we already know with certainty. As the authors discuss, cannabis undisputedly results in dose-dependent cognitive and motivational problems. If we are preaching physical therapy and home exercise to counter deconditioning, socialization to reverse depression, cognitive-behavioral therapy to increase coping, returning to work to prevent prolonged disability, and other active measures to prevent pain from becoming chronic, then why would we suggest treatments known to blunt motivation, energy, concentration, and overall mood? As a general central nervous system suppressant,⁴ cannabis works broadly against our best efforts to rehabilitate patients and restore their overall function.

ALL CANNABIS IS NOT THE SAME

The authors use the general term cannabis in their title, yet rightly unpack the differences between medical marijuana, tetrahydrocannabinol (THC), and cannabidiol (CbD). However, in the minds of untrained and pain-stricken patients seeking rapid relief and practical solutions, such distinctions are likely irrelevant.

The danger in the barrage of publications examining cannabis vs medical marijuana vs THC vs CBD is that they all communicate an unintentional yet problematic message: that marijuana of some sort for pain is acceptable to try. And in the face of financial pressures, changing legal landscapes, insurance coverage volatility, and access issues, are patients really going to always secure prescriptions for wellregulated CBD (lacking psychoactive THC) from thoughtful and well-informed physicians, or will they turn to convenient street suppliers?

Simplified perceptions of safety and efficacy across all cannabis products do not help. More troublesome would be to extrapolate safety to other forms of marijuana known to be dangerous, such as synthetic cannabinoids, which in some instances have been associated with catastrophic outcomes.⁵ The slippery slope is real: if the message becomes that some (or most) marijuana is benign or even therapeutic, what is to curb a widespread and unregulated epidemic?

YOUTH AT RISK

Some groups are more vulnerable than others to the potential negative effects of cannabis. In a study at a medical cannabis dispensary in San Francisco,⁶ adolescents and young adults used more marijuana than older users did and had higher rates of “use when bored” and eventual pharmacologic dependence. Sustained use of marijuana by young people places them at risk of serious psychiatric disorders, with numerous studies demonstrating the unfolding of schizophrenia, depression, bipolar disorder, and more.⁷

As the authors point out, cannabis may be contraindicated in those already burdened with mental health problems. If we recall that comorbid psychiatric disorders are the norm rather than the exception in chronic pain conditions,⁸ can we recommend cannabis therapy for most patients with chronic pain with confidence that it will not cause unintended problems? Evidence already shows that even well-established medical marijuana services attract (and perhaps unintentionally debilitate) a certain high-risk demographic: young, socioeconomically disadvantaged men with other comorbid psychiatric and substance use disorders, who ultimately rank poorly in functional health measures compared with the general population.⁹

NOT REEFER MADNESS, BUT REEFER CAUTION

I am not advocating the fear-mongering misinformation campaigns of the past. We should not exaggerate and warn about “reefer madness” or equate marijuana with untruths about random violence or complete bedlam. Nonetheless, concerns for widespread amotivation, worsening psychiatric states, chronic disability, and chemical dependence are very real.

Needed are tightly regulated, well-controlled, and long-term prospective studies involving isolated CBD formulations lacking THC. Over time, perhaps only formulations approved by the US Food and Drug Administration will be embraced. In the meantime, more comprehensive approaches should be recommended, such as team-based interdisciplinary rehabilitation programs that have shown efficacy in handling chronic pain complexities.^10,11

If such steps are unlikely, physicians should nonetheless stand united in sending a message of cautious optimism regarding medical marijuana, educating their patients not only about recently advertised potential yet inconclusive benefits, but also about the well-known and actual certitudes of its harms for use in chronic pain management. There is plenty of bad and worse information to share with patients, and there is a slippery slope of epidemic proportions to be wary about.