Everyone has nightmares sometimes. But for people with PTSD, it's different.

Sam Brace doesn't want to talk about what he saw when he was a soldier in Iraq eight years ago. In fact, it's something he's actively trying not to dwell on. But what he can't control are his dreams.

They're almost always about the same explosion. "When I was overseas, we'd hit an IED," Brace says. "When I have a nightmare, normally it's something related to that."

Healthy dreams seem kind of random, according to Steven Woodward, a psychologist with the National Center for PTSD at the VA Medical Center in Menlo Park, Calif. "They're wacky," he says. "They associate lots of things that are not normally associated."

PTSD dreams are the same real-life event played over and over again like a broken record. "Replicative nightmares of traumatic events ... repeat for years," Woodward says. "Sometimes 20 years."

Scientists wanted to find out the reason why people with PTSD can't sleep and dream normally. One theory comes from Matthew Walker, a psychology researcher at the University of California, Berkeley. His particular interest lies in rapid eye movement, or REM. It's the time during sleep when a lot of dreaming occurs.

It's also a time when the chemistry of the brain actually changes. Levels of norepinephrine — a kind of adrenaline — drop out completely. REM sleep is the only time of day when this happens. That struck Walker as a mystery. "Why would rapid eye movement sleep suppress this neurochemical?" he asks. "Is there any function to that?"

Walker found that in healthy people, REM sleep is kind of like therapy. It's an adrenaline-free environment where the brain can process its memories while sort of stripping off their sharp, emotional edges. "You come back the next day, and it doesn't trigger that same visceral reaction that you had at the time of learning."

Emotions are useful, he says. They show us what really matters to us. "But I don't think it's adaptive to hold onto that emotional blanket around those memories forever," he says. "They've done their job at the time of learning, then it's time to hold on to the information of that memory, but let go of the emotion."

Walker's theory suggests that in people with PTSD, REM sleep is broken. The adrenaline doesn't go away like it's supposed to. The brain can't process tough memories, so it just cycles through them, again and again.

So, what if you could make the adrenaline just go away? Enter prazosin.

Pfizer Inc. introduced the drug under the brand name Minipress in the 1970s to treat high blood pressure. Dr. Murray Raskind, a VA psychiatrist in Seattle, says the drug, now generic, can cost anywhere between 5 and 15 cents. And, actually, it's not terribly effective as a blood pressure medication, he says.

But what prazosin does do is make people less sensitive to adrenaline. About a decade ago, Raskind starting giving prazosin to some of his PTSD patients, including one Vietnam War veteran.

"He had this recurrent nightmare of being trapped by the Vietcong forces in a landing zone and having his best friend killed in front of his eyes by a mortar round," Raskind says.

After a few weeks of treatment with prazosin, the veteran came in for a follow-up appointment. Raskind says the veteran told him that he wasn't sure the medication was working. He was still having the same dream over and over — just about something else. He told Raskind that in the new dream he was in his fifth grade classroom and there was a test. If he didn't pass the test, he wasn't going to be promoted to the next grade. But he never even got the assignment.

"I said, 'That's my nightmare!' " Raskind says.

Indeed, the veteran's new dream was the stress dream of a healthy brain trying to work things out, Raskind says.

This year, the VA is expected to finish up its trial for prazosin. It's already prescribing the drug to about 15 percent of its PTSD patients. Raskind, of course, would like to see that number rise.

"To us, it's a simple thing that works," he says.

Copyright 2012 KQED