A year after the first sizable controlled trial on the effectiveness of cannabinoids in managing epileptic seizures was published, a 36-study review has confirmed evidence for effectiveness, but so far only for younger patients.
Growing acceptance that cannabis has medical benefits is contributing to a widespread rollback of laws against the drug. However, the legacy of the drug's long prohibition is a lack of hard evidence for the effectiveness of cannabis, and the compounds that make it up, because it is so hard to win approval to study a drug you can go to jail for consuming.
Anecdotal accounts of marijuana consumption reducing epileptic fits are widespread, contributing to decisions to loosen restrictions on the drug in Australia, among other places. In the quest to add some rigor to the debate, Dr Emily Stockings of the University of New South Wales conducted a systematic review, published in the Journal of Neurology, Neurosurgery and Psychiatry, of everything medical journals have published on the topic. She found consistent evidence that compounds from cannabis often reduce the average frequency of epileptic seizures for children and teenagers where conventional anti-convulsive drugs have failed. Almost half those involved in the study experienced at least a 50 percent decrease in seizures.
Thirty-six studies sound like a lot, but of these only six were random controlled trials, where cannabis or its components were compared with a placebo. The rest were purely observational, sometimes of a single case, and therefore of much lower value.
“We even included the bad studies, but we weighted them by quality," Stockings told IFLScience. "We used everything that looked at cannabis and epilepsy, unless it was an opinion piece without actual data.”
Randomized controlled trials on the topic date back to 1980, but until last year the largest had just 15 participants. Even the three recently-published trials had modest numbers, but gain credibility from the consistency of their results.
Stockings told IFLScience few of the studies looked at the effects on adults, and those that did were of insufficient quality to draw conclusions. She attributed the predominance of childhood studies to the fact the mortality rate in the most severe cases is so high that many in greatest need don't survive to adulthood. There is also strong pressure for research from parents.
We should soon have much better data, as 10 more studies are currently underway. This is encouraging because the paper notes we know very little about the ideal dosage for the drug. Moreover, there is some evidence it works best in conjunction with the common epilepsy treatment clobazam, but this requires further research, as does a comparison of whether cannabis extracts outperform other treatments even for those that respond to conventional drugs.