CHICAGO -- Viagra's effect in women has been disappointing, but a new small study finds those on antidepressants may benefit from taking the little blue pills. The research involving 98 premenopausal women found Viagra helped with orgasm. But the benefits did not extend to other aspects of sex such as desire, researchers report in Wednesday's Journal of the American Medical Association.

"For women on antidepressants with orgasm problems, this may provide some wonderful relief," said psychologist Stanley Althof, director of the Center for Marital and Sexual Health of South Florida in West Palm Beach, who was not involved in the study. "But it will not improve their desire or arousal."

Antidepressants can interfere with sex drive and performance even as the drugs help lift crippling depression. Switching drugs or reducing the dose can help. But many people, men and women, stop taking them because of their sexual side effects.

The complaints are common. More than half the people who take antidepressants develop sexual problems, prior studies have found, especially for people taking Prozac, Paxil, Celexa and other drugs that work by increasing the chemical serotonin in the brain. Serotonin is thought to slow down orgasm, perhaps by diminishing the release of another brain chemical, dopamine. Viagra increases blood flow to sex organs.

Pfizer Inc. spokeswoman Sally Beatty said the company currently has no plans to pursue FDA approval for using its drug Viagra as a treatment for female sexual dysfunction. The company ended its internal research on Viagra for women in 2004. While Viagra was found to be safe, the results were inconclusive, Beatty said in an e-mail.

The search for a Viagra equivalent for women has been disheartening. A testosterone patch was sent back for more safety study by the Food and Drug Administration. A handheld vacuum device that increases blood flow to the clitoris does have FDA approval, and BioSante Pharmaceuticals Inc. is testing a testosterone gel called LibiGel.

The new Viagra findings are based on an eight-week experiment. The 98 women were using antidepressants successfully but were having sexual problems. Their average age was 37.

The women agreed to attempt sexual activity at least once each week. Each time, they took a pill, not knowing whether it was Viagra or a matching dummy pill.

While 72 percent of the women taking Viagra reported improvement on an overall scale, only 27 percent of the women taking the placebo reported improvement.

Althof said it's "worrisome" that 43 percent of the women on Viagra experienced headaches, compared to 27 percent of the women on dummy pills. Indigestion and reddening of skin (flushing) also were reported more often by the women taking Viagra.

Psychologist Leonore Tiefer of New York University School of Medicine said industry-funded research has oversimplified women's sexual experience. She noted the new study, funded by a Pfizer grant, found more side effects than benefits.

"Where's the question to the women: Is it worth it?" Tiefer said.

An earlier study in men taking antidepressants found more pronounced sexual benefits with Viagra than the benefits found for women, said lead author Dr. George Nurnberg, a psychiatrist at the University of New Mexico School of Medicine in Albuquerque.

But the message for men and women who need antidepressants is that Viagra may help them stay on the drugs, he said.

"We're not talking about a lifestyle issue. We're talking about a medical necessity issue," Nurnberg said.

Pfizer had no influence on the design, findings or manuscript, Nurnberg said. He and several of the other authors disclosed financial ties to Pfizer and other drugmakers.

(Copyright 2008 by The Associated Press. All Rights Reserved.)