The couple, working with other researchers, will treat no more than 24 veterans with the therapy, following Food and Drug Administration protocols for testing an experimental drug; MDMA is not approved for any medical uses.

A handful of similar experiments using MDMA, LSD or marijuana are now in the works in Switzerland, Israel and Britain, as well as in this country. Both military and civilian researchers are watching closely. So far, the research has been largely supported by nonprofit groups.

“When it comes to the health and well-being of those who serve, we should leave our politics at the door and not be afraid to follow the data,” said Brig. Gen. Loree Sutton, a psychiatrist who recently retired from the Army. “There’s now an evidence base for this MDMA therapy and a plausible story about what may be going on in the brain to account for the effects.”

In interviews, two people who have had the therapy — one, Anthony, currently in the veterans study, and another who received the therapy independently — said that MDMA produced a mental sweet spot that allowed them to feel and talk about their trauma without being overwhelmed by it.

“It changed my perspective on the entire experience of working at ground zero,” said Patrick, a 46-year-old living in San Francisco, who worked long hours in the rubble after the Sept. 11, 2001, attacks searching in vain for survivors, as desperate family members of the victims looked on, pleading for information. “At times I had this beautiful, peaceful feeling down in the pit, that I had a purpose, that I was doing what I needed to be doing. And I began in therapy to identify with that,” rather than the guilt and sadness.

The Mithoefers administer the MDMA in two doses over one long therapy session, which comes after a series of weekly nondrug sessions to prepare. Three to five weeks later, they perform another drug-assisted session; and again, patients engage in 90-minute nondrug therapy before and after, once each week.