Updated | A blood pressure drug that one in six veterans with PTSD may take to control their nightmares may not work better than a placebo, new results published in the New England Journal of Medicine suggest. Despite the results, the researchers still believe the drug might work—just for some people.

The study followed more than 300 people, half of whom took the drug and half of whom took a placebo, for six months. About 80 percent had received disability for PTSD. Almost all were men who had fought in Vietnam.

Despite taking a relatively high dose, the researchers found prazosin reduced people’s score on one item of a PTSD assessment test related to distressing dreams—but a placebo did that, too, and just as well. Neither did the drug help people sleep better.

“I was very surprised,” Dr. Murray Raskind told Newsweek. Raskind, a psychiatrist associated with the Veterans Affairs Puget Sound Health Care System, first began studying prazosin more than 20 years ago. In 1995, he was treating a Vietnam veteran for nightmares; this veteran also had high blood pressure. First, he tried one drug, a beta-blocker, which made the nightmares worse. Then, he tried prazosin.

In theory, prazosin ought to subdue nightmares because it blocks the alpha-1 receptor for adrenaline and related chemicals in the brain. This system is also involved in sleep—so disruptions might be behind the nightmares, Raskind said. “It’s possible that out of these disruptions occur these trauma nightmares, which are very different in quality from normal bizarre or fantastical dreams, whether pleasant or unpleasant.”

Trauma nightmares are more vivid, he noted, and people waking up from these nightmares can be sweating, have an increased heart rate, and be anxious. “What prazosin does is to bring back down to normal the brain norepinephrine or adrenaline-like activity.”

In 2010, an American Academy of Sleep Medicine task force recommended that prazosin could be used to treat nightmares linked with PTSD—a recommendation made based on “a substantial amount of high quality evidence and/or based on a consensus of clinical judgment.” Some previous studies—including one in 2013 that Raskind also did—have shown that prazosin can improve veterans’ sleep. (There have been six positive studies for the drug, he said, which is associated with some minor side effects like dizziness and feeling lightheaded.)

The chair of NYU Langone Health’s psychiatry department, Dr. Charles Marmar, agreed that despite this study's negative results, prazosin may still have a place in PTSD treatment. (Marmar was not involved in this study, but is familiar with Raskind and his work.) “All combat trauma in America constitutes 15 percent of PTSD; 85 percent of all PTSD cases are civilian,” he said—civilians are more likely to have acute PTSD from a single event like 9/11 rather than chronic PTSD from a war zone, he noted. “And the data look pretty good on prazosin for civilians.”

That may be because combat trauma is different than other types of trauma: “I wouldn’t be at all discouraged from using this drug in a VA population,” Marmar said. And perhaps the drug only works for people who have higher blood pressure than their peers, Raskind said; that wasn’t necessarily the case for the people in this study.

About 100,000 veterans treated within the VA who were diagnosed with PTSD were receiving prazosin. Since 2002 the number of prescriptions has been rising every year, Raskind noted. This study would probably not have a major impact on that trend, Marmar said—especially because the effects can be remarkable. 

“One of my patients had nightmares, three times a week, for 49 years," Marmar said. "When I treated him with prazosin, they dropped down to having nightmares once every two to three weeks.”

"It's amazing to help someone who suffered for five decades."

This article has been updated to reflect Dr. Marmar's affiliation with NYU Langone Health.