For neuropathic pain, marijuana yields modest benefits

As medical marijuana penetrates mainstream medical practice in the United States and elsewhere, awareness of the potential benefits, potential risks, local laws governing its use for treatment or chronic pain gain importance, according to a specialist reviewing available data at Pain Care for Primary Care.

For many specific types of chronic pain more data are needed to judge the benefit-to-risk ratio of marijuana relative to other options, but there are reasonable data suggesting both acceptable safety and meaningful efficacy of this analgesic in neuropathic pain, according to the associate professor in the departments of anesthesia and family medicine, McGill University, Montreal.

In neuropathic pain, the evidence includes at least five randomized trials. In a recently published review article for which he served as senior author, the degree of neuropathic pain reductions were characterized as being on an order similar to those achieved with opioids and anticonvulsants. In one study, the number needed to treat for a 50% pain reduction was just 2.

In Canada, marijuana is now available for at least some medical uses in every province. In the United State, 23 states have passed laws permitting clinical use of marijuana, according to suggestion that legalization of marijuana has fueled a growing acceptance of marijuana as a treatment option whether or not it is prescribed. For this reason, it's necessary to examine the objective evidence to provide appropriate counseling.

We are past the point where this option can simply be ignored. Even if they do not intend to prescribe marijuana for chronic pain, clinics should become familiar with evidence regarding benefit and safety as well as the laws regarding its use.

In a study of long-term safety, a standardized cannabis product containing 12.5% tetrahydrocannabinol was dispensed to 215 current or prior users of marijuana with a noncancer chronic pain syndrome.

Followed for one year, adverse events in this group were compared with 216 control patients who also had chronic pain but were not using cannabis.

The odds ratio of nonserious adverse events in the categories of respiratory disorders, infectious disorders, nervous system disorders, and psychiatric disorders were all significantly higher in the group treated with cannabis, but almost all were judged to be of mild to moderate severity. There was no significant difference in the risk of serious adverse events. It was also reported there was no difference between the cannabis group and controls for neurocognitive testing at baseline, six months, or the end of one year.

Pain control was also monitored over the course of the study. Average pain scores in the cannabis group fell modestly but consistently over the course of the study. Over the same period, the pain scores rose slightly in the control group.

There is a long list of unanswered questions regarding effective use of marijuana in the control of chronic pain. For example, it was noted that the optimal composition of cannabinoids has yet to be determined. It was noted that more than one of the complex constituents may contribute to pain control, and these constituents are not necessarily the same as those most favored by recreational users seeking a euphoric “high.”

There is also a long list of unanswered questions about safety. Reviewed some evidence that inhaled vaporized marijuana may be safer than traditional smoked marijuana because of reduced exposure to toxins, but suggested more rigorous studies are needed to generate objective data that can better quantify the benefits to risk of this and other methods of marijuana delivery.

Despite unanswered questions, marijuana is widely available and likely to be considered by pa- tients for chronic pain whether or not it is recommended by physicians. It is for this reason that clinicians need to become familiar with both its potential risks and benefits.

It will be helpful to patients if they can be provided practical and accurate information about what is and is not known about this treatment.