This is a relief for the drugmaker, which faced repeated setbacks in gaining agency approval and needs to replace revenue that will be lost when patents on Effexor XR - a $3.8 billion moneymaker - start to expire this year.

Whether Pristiq will prove to be a true lifesaver for Wyeth - let alone depressed patients - is another matter. Pristiq is, essentially, a reworked version of Effexor, which is in a class of antidepressants known as SNRIs. (These work slightly differently than the SSRI class, which includes Paxil, Prozac and Zoloft). For this reason, Wall Street is divided over Pristiq’s ability to generate big dollars. In an investor note this week, Credit Suisse analyst Catherine Arnold, for instance, forecast $480 million in revenue by 2012, while Bear Stearns analyst John Boris predicts Pristiq may hit the billion-dollar mark.

Nonetheless, for Wyeth, the approval is welcome news. The next big hurdle for the drugmaker is winning FDA approval to market Pristiq to treat hot flashes caused by menopause. As with the indication for depression, Wyeth has faced repeated delays at the agency and it remains unclear how this will play out.