Repeated use of the drug popularly known as "ecstasy" significantly raises the risk of developing sleep apnea in otherwise healthy young adults with no other known risk factors for the sleep disturbance, a new study by Johns Hopkins scientists suggests. The finding is the latest highlighting the potential dangers of the amphetamine-style chemical, currently used illegally by millions of people in the United States.

The Johns Hopkins scientists note that sleep apnea itself can lead to an assortment of health problems, including a decline in cognitive function, an increased risk of diabetes, and an increased risk of death from heart disease.

"We know that abusing drugs can have numerous harmful effects. Our findings show yet another reason not to use ecstasy," according to lead researcher Una D. McCann, M.D.

Users claim the drug enhances intimacy, diminishes anxiety, and facilitates some forms of psychotherapy.

The team led by McCann, professor in the Department of Psychiatry at the Johns Hopkins University School of Medicine, previously linked ecstasy, or methylenedioxymethamphetamine (MDMA), to a variety of neurological problems, including subtle cognitive deficits, impulsive behavior, and altered brain wave patterns during sleep. These problems are thought to arise from the drug's targeted toxic effects on neurons that produce the hormone serotonin. Studies in animals and people have shown that MDMA use shortens the filament-like ends of these nerve cells, preventing them from making normal connections with other neurons.

Because these cells regulate multiple aspects of sleep, McCann's team recruited 71 sleep study volunteers, all MDMA users, by advertising for "club drug users" in newspapers and fliers. All had typically used other recreational drugs as well. They also recruited 62 participants who had similar patterns of illegal drug use but had never taken MDMA. The MDMA users had taken the drug at least 25 times in the past, a number previously shown to have lasting effects on serotonin neurons. All of the volunteers were otherwise physically and mentally healthy and had abstained from drug use for at least two weeks prior to the study.

To evaluate the participants' breathing patterns during sleep, each volunteer spent a few nights at a sleep research center. From "lights out" at 11:00 p.m. to "lights on" at 7:00 a.m., study volunteers slept while hooked up to a variety of devices to measure breathing, including airflow monitors at their noses and mouths and bands around their chests and abdomens to measure expansion.

The researchers diagnosed sleep apnea by counting the rate of incidences of shallow or suppressed breathing, with mild apnea requiring five to 14 of these incidences, moderate apnea requiring 15 to 29, and severe apnea requiring 30 or more.

Results published in the Dec. 2, 2009, issue of Neurology, the medical journal of the American Academy of Neurology, showed that rates of mild apnea were similar between the two groups, with 15 MDMA users and 13 other volunteers affected. However, while 8 MDMA users had the moderate form of apnea and 1 had the severe form, none of the other volunteers had either of these more serious forms. Results showed that the more participants had used MDMA in the past, the more severe their apnea was likely to be.

Known risk factors for sleep apnea include older age, obesity, and other medical conditions. However, McCann says, of the 24 ecstasy users who had sleep apnea, 22 were age 31 or younger, and none had any known serious medical problems.

"Our subjects were otherwise healthy young adults, so this is a very surprising finding," she says.

Though the researchers suspect that the cause for the MDMA users' sleep apnea centers on affected serotonin neurons, the exact mechanism remains a mystery. McCann explains that these neurons appear to help sense blood oxygen levels, control airway opening and generate breathing rhythms. Any of these pathways could be separately influenced by ecstasy use, she says. The researchers are currently working to tease apart which pathway is at play in MDMA users.