Four years ago, he moved on to humans. In a study of 30 subjects who were terrified of heights, he found the drug significantly better than standard treatment.
"It worked spectacularly," says Davis. "There was a fourfold increase in effectiveness." Since then, other studies have shown that D-cycloserine can also help with social anxiety and obsessive-compulsive disorder.
Two months ago, largely for his work on D-cycloserine, Davis won the Scolnick Prize in Neuroscience from MIT, awarded every year to a researcher who has done outstanding work.
"There's an increasing amount of data to support the idea that this could be really important," says NIH neuroscientist Dr. Daniel Pine, an anxiety expert. Along with colleagues at Johns Hopkins Hospital, Pine has started a study to find out whether D-cycloserine can help intensely shy children learn to be more outgoing.
In anxiety disorders, D-cycloserine is not used alone but combined with a treatment called exposure therapy. The treatment puts patients through the experience they fear, teaching them that their dread is exaggerated.
Such therapy is not new. It can work, but it is often terrifying and lengthy, and many patients drop out before their fears diminish. Davis and others say D-cycloserine can speed up the process.
Scientists aren't sure how the drug works. The main theory: By juicing NMDA, the drug helps the brain cement newly acquired learning from exposure therapy.
The D-cycloserine research adds evidence for an emerging view of how people overcome anxiety. Until recently, scientists thought the key was to somehow "erase" fear. But most researchers now think people succeed by acquiring new knowledge - for example, that riding an elevator will not kill you.
"The new idea is that anxiety disorders are in part a learning disorder. Think of D-cycloserine as a learning aid," says Johns Hopkins University child psychiatrist Mark Riddle, who is working with Pine on the anxiety study.
A key piece of evidence for this theory: Patients need only a few doses of D-cycloserine, which must be taken around the time of exposure therapy.
"On its own, it does nothing," says Otto.
In this respect, D-cycloserine differs from other drugs used to treat fear-related conditions. These medicines - anti-anxiety drugs such as Xanax or antidepressants such as Prozac - work without therapy.
