WASHINGTON (October 4, 2012)--More Americans than ever are taking generic versions of such blockbuster medicines as Plavix and Lipitor, which are now available in low-cost versions.

But the government's revelation that it mistakenly approved a defective generic antidepressant could revive longtime concerns about the safety and quality of knockoff drugs.

On Wednesday the U.S. Food and Drug Administration asked Teva Pharmaceuticals to withdraw its drug Budeprion XL 300 after tests showed it did not properly release its key ingredient.

The decision came after years of complaints by patients about headaches, anxiety and other side effects from the drug, which was sold as a generic equivalent to GlaxoSmithKline's Wellbutrin.

The news threatened to undermine years of outreach by the government and drug makers to assure patients that generic drugs are just as effective as brand-name drugs.