Jury still out on medical marijuana for chronic pain and PTSD

Some say there’s a fine line between pleasure and pain, but the line between pleasure and pain relief could well be so fine as to be almost meaningless when it comes to making a dispassionate assessment of the merits of medical marijuana.

The bottom line of two new studies of previous studies, published in the journal Annals of Internal Medicine, is that scientific evidence is simply too limited to make firm conclusions about the effectiveness and safety of cannabis and cannabinoid products in treating chronic pain or post-traumatic stress syndrome (PTSD).

While that’s not a tick for medical marijuana, it’s not necessarily a cross either – not without more study, at least. The only thing that can be said with any certainty is that the two papers – on chronic pain and PTSD – demonstrate the haze that envelops science and society when an otherwise illegal substance is made legal to access on a therapeutic basis.

}The studies focused on the particular maladies of chronic pain and PTSD because the research was funded by the US Department of Veterans Affairs, with both analyses led by Maya O’Neil, Shannon Nugent and Benjamin Morasco of the VA Portland Health Care System in Oregon.

That’s presumably because former military personnel suffering undeniable physical and psychological injuries are among the increasing numbers of Americans asking a doctor to prescribe cannabis in the 28 states and the District of Columbia that have now legalised it for medical purposes. (That’s 20 more states than those that have also legalised the recreational use of cannabis.)

Pain management, as noted in the pain-focused study, is the reason cited by 45–80% of people seeking medical cannabis. Based on 13 systematic reviews and 62 primary studies, it concludes there is “low-strength” evidence to suggest cannabis might alleviate neuropathic pain “in some patients” but insufficient evidence for other types of chronic pain: “Most studies are small, many have methodological flaws, and the long-term effects are unclear given the brief follow-up of most studies.”

The implication of finding neuropathic pain relief “in some patients” is worth considering. “Possible interpretations are that cannabis is simply not consistently effective,” the authors write, “or that, although cannabis may not have clinically important effects on average, subgroups of patients may experience large effects. We did not find data to clarify which subgroups of patients are more or less likely to benefit.”

The PTSD study, based on two systematic reviews and three primary studies, likewise found “insufficient evidence to draw conclusions about potential benefits and harms of cannabis use in patients”. Despite the limited research, the paper notes, many US states have allowed medicinal use of cannabis for PTSD, with many press reports about individuals helped by it. These reports are not enough to determine whether cannabis reduces symptoms, however or to distinguish between effects of the drug, placebo effects and the natural course of symptoms.

This leaves medical doctors, both papers conclude, in the position of needing to engage in “evidence-based discussions” with patients choosing to use or request cannabis, weighing up the potential perceived benefit against the known and unknowns of potential harms, with there being “low- to moderate-strength” evidence that cannabis use is associated with an increased risk for psychotic symptoms and short-term cognitive dysfunction.

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