Wyeth-Ayerst drug takes aim at severe depression, Prozac. (American Home Products Corp. Wyeth-Ayerst Laboratories Division's Effexor)

ST. DAVIDS - The anti-depressant drug market is booming.

With Eli Lilly and Co.'s Prozac and other new depression drugs reaching celebrity status and stratospheric sales, Wyeth-Ayerst Laboratories recently introduced its own drug to battle severe depression.

Effexor, the newest of these wonder drugs, recently gained approval by the Food and Drug Administration and is now on pharmacy shelves. Wyeth-Ayerst touts Effexor as a "breakthrough" prescription product with reduced side effects and added strength over current drugs designed to treat severe depression.

It's been estimated that depression affects 17.6 million U.S. adults. Less than a third seek and receive treatment. Millions more go undiagnosed. Federal government researchers also estimate that only about 75 percent of the individuals suffering from depression benefit from the medications currently on the market.

According to the Agency for Health Care Policy and Research, depression cost the United States an estimated $27 billion in 1989. More than $17 billion of that was due to lost work time.

Prozac, the best-known of the new drugs, is set to break the $1 billion in sales mark for the second year in a row. Prescriptions for Prozac and its rivals, Zoloft and Paxil, are leaping by 45 percent per year. The three drugs are drumming up huge sales with aggressive campaigns to reach the legions of people with depression who don't seek treatment.

The Genesis Report, a newsletter that tracks the pharmaceutical industry, predicts Effexor will grab a 7 percent share of the market from the other three drugs in 1994 and an 11 …