Depression Remedy OKd for U.S. Sales : Drugs: Effexor, in trials, helped some patients who did not respond to the popular Prozac.

Psychiatrists have a new weapon against depression, one some doctors are calling “Prozac with a boost” because it acts on a second brain chemical as well as the one affected by Prozac.

The Food and Drug Administration this week approved Effexor for treatment of depression. It is to be labeled a “structurally novel antidepressant.”

Unlike other drugs, Effexor acts on two crucial brain chemicals that affect depression, without causing serious side effects, according to the manufacturer, American Home Products Corp.

“Our most striking finding was that it worked well on patients who previously were non-responsive” to other depression remedies, said Dr. John Feighner of San Diego, a psychiatrist who evaluated Effexor in clinical trials.

Depression is the most prevalent mental health problem, afflicting about 15 million Americans at some time in their lives. Antidepressant drugs have become an $8-billion industry.

The most widely prescribed is Prozac, made by Eli Lilly & Co. It, as well as two similar drugs--Pfizer’s Zoloft and SmithKline Beecham’s Paxil--act on a neurotransmitter called serotonin and produce minor side effects.

Earlier depression drugs affected more brain chemicals and also caused more serious side effects, from weight gain to heart trouble.

Effexor seems to have found a middle ground. It affects serotonin and a second neurotransmitter, norepinephrine, but does so precisely enough that it produces no more side effects than the serotonin-only drugs, said Dr. Richard Rudolph, senior research director for Effexor.

Doctors don’t know a lot about how neurotransmitters relate to depression. They suspect that some patients may be affected by one brain chemical and others by another, so some may need a drug with more than one target.

“The hope is, and the expectation is, that because Effexor affects two neurotransmitters, its actions would be broader,” Rudolph said. “We don’t want to mislead with a broad statement that it’s more effective than Prozac, but there’s a lot of interest in this drug--a lot of interest in having alternative, additional therapies.”

In five clinical trials, Effexor alleviated depression in 70% to 75% of patients, according to company data. About 10% of depressed people do not respond to drugs, but Feighner’s study found that Effexor helped between 35% and 40% of patients previously deemed untreatable.

Shares of New York-based American Home Products added 12.5 cents to $65 on the New York Stock Exchange.