Medical Marijuana: Analysis Says Not Effective for Pain, Doctor Says Prescribe Anyway

An analysis in Canadian Family Physician casts further doubt on the ability of marijuana to provide pain relief for patients with chronic noncancer pain (CNCP). Yet, in an accompanying editorial in the same issue, Roger Ladouceur, MD, Associate Scientific Editor of CFP, suggests that pain management specialists continue to prescribe it.

First, the analysis. The researchers looked at six randomized controlled trials involving 226 patients. Five of the studies assessed the use of medical marijuana in neuropathic pain as an adjunct to other concomitant analgesics including opioids and anticonvulsants. The five trials were considered to be of high quality; however, all of them had challenges with masking. The study found that low-dose medical marijuana can be used in refractory neuropathic pain in conjunction with traditional analgesics.

“However,” the review authors noted, “trials were limited by short duration, variability in dosing and strength of delta-9-tetrahydrocannabinol, and lack of functional outcomes. Although well tolerated in the short term, the long-term effects of psychoactive and neurocognitive effects of medical marijuana remain unknown. Generalizing the use of medical marijuana to all CNCP conditions does not appear to be supported by existing evidence. Clinicians should exercise caution when prescribing medical marijuana for patients, especially in those with non-neuropathic CNCP.”

Studies were included if they evaluated the effect of smoked or vaporized cannabinoids (nonsynthetic) for CNCP and were designed as a controlled study involving a comparison group, either concurrently or historically. Pain scores were extracted using the visual analogue scale (VAS) or an alternative numerical pain rating tool. If pain scores were not reported, surrogate measures of effectiveness were included (sleep, function, and quality of life). Frequency of serious and most commonly reported adverse effects was collected.

All studies reported a statistically significant benefit in terms of pain relief. But while most of the trials were of high quality, the psychoactive effect of delta-9-THC versus inactive placebo resulted in unmasking in many trials, according to the review authors.

“Only two studies reported maintaining a positive but smaller effect size when correcting for this factor, consistent with the finding that inappropriate blinding has been shown to cause larger treatment effects,” they explained.

Other issues were identified with the studies, notably the difference between reduction in pain and clinically meaningful pain reduction. Finally, the amount of exposure to delta-9-THC in all studies was extremely low in contrast to that available in the marketplace.

The accompanying editorial, however, addressed a key point about other CNCP interventions. According to Dr. Ladouceur, “Some will say that we should not get involved because marijuana is ineffective. Yet, are the other medications that we prescribe for chronic pain more effective? If this were true, would chronic pain still be an issue? I am not so sure that the substances we prescribe have fewer personal and societal side effects. Marijuana would not be the first product prescribed with the goal, basically, of minimizing personal and societal consequences. Is that not what we do when we prescribe methadone?”

While acknowledging that the clinical evidence in support of prescribing marijuana is limited, the editorial makes the case that physician involvement in prescribing it avoids a situation in which patients who say that the drug offers them relief are forced to get it wherever and however they can. Further, it would allow for some control over patient consumption and the ability to gather more evidence on the composition, strength, quality, or potential long-term side effects of its use.