The medical marijuana movement has been blowing up all around the world. Both ancient and modern studies have cited it as a cure for all sorts of ailments ranging from chronic pain to even leprosy (in the ancient Indian science of ayurveda too, of all places).

But recent research shines a light on the darker side of the use of marijuana for medicinal purposes. Conducted by psychologists from University of Michigan Medical School and the VA Ann Arbor Healthcare System, the new study has found that more than half its participants who used medical marijuana products to ease pain also experienced clusters of multiple withdrawal symptoms when they were between uses. And a tenth of the participants even experienced worsening changes to their sleep, mood, mental state, energy, and appetite over the next two years as they continued to use cannabis.

Published in the journal Addiction, the research was conducted over a period of two years, and reports findings from detailed surveys of 527 residents of Michigan in the U.S., all of whom qualified under the state’s system to permit medical use of marijuana to people with certain conditions and non-cancer related pain. [Read more at VICE]