Anecdotes about marijuana’s power against epilepsy abound. This week, a rigorous clinical trial threw its weight behind them, STAT reports. Children and teenagers with Dravet syndrome, a devastating form of the seizure disorder, received an oral solution of cannabidiol, a component of marijuana, while a control group got a placebo. For those in the treatment group, the number of seizures per month was cut roughly in half, on average, compared to a negligible decline in the placebo group, researchers reported this week in The New England Journal of Medicine. But cannabidiol wasn’t without problems. Side effects, including vomiting and elevated liver enzymes, were bad enough that eight kids withdrew from the trial. Testing continues, as researchers want to understand the drug’s long-term effects and why it helps some children more than others.