New research shows that users of the drug ecstasy may face an increased risk of a potentially dangerous sleep disorder.
Ecstasy has been found to bring on breathing problems and significantly raise the risk of sleep apnoea even among previously healthy users.
Sleep apnoea is a common condition that has been linked to strokes, heart attacks, diabetes and mental impairment.
The US study involved two groups of participants - 71 volunteers admitted having taken ecstasy 25 times or more, while 62 had used other drugs but not ecstasy.
Researchers tested their breathing and nasal pressure while they were asleep and found that both groups showed similar rates of mild sleep apnoea.
But moderate and severe forms of the condition were found only among ecstasy users. The longer the participants had taken the drug, the more severe their condition was.
Study leader Dr Una McCann, from The Johns Hopkins School of Medicine in Baltimore, said: "People who use ecstasy need to know that this drug damages the brain and can cause immediate and dangerous problems such as sleep apnoea.
"Our findings may be explained by how ecstasy damages neurons related to serotonin, a chemical in the brain that is involved in sleep regulation and breathing, among other important functions."
The findings are published in the journal Neurology.