The Food and Drug Administration approved AstraZeneca's once-daily schizophrenia drug, Seroquel XR.
Seroquel is AstraZeneca's second-biggest drug, with global sales of $3.4 billion last year.
The approval is a welcome boost to AstraZeneca after the recent high-profile failures of two new drugs for stroke and heart disease.
The company is looking to established drugs such as Seroquel to keep the business growing while it seeks additional acquisitions.
In addition, the original immediate-release formulation of Seroquel faces patent threats, with a case potentially coming to court next year in the United States.
Seroquel belongs to a class of drugs called atypical antipsychotics and is the most prescribed treatment of its kind in the United States. It is also used in patients with bipolar disorder.