Eli Lilly & Co. said Symbyax should arrive in most U.S. pharmacies in two to three weeks, the Indianapolis Star reported Monday.

Symbyax becomes the first FDA-approved drug to treat the depressive phase of bipolar disorder, a hard-to-treat mental illness with debilitating mood swings ranging from deep depression to abnormal elation.

Symbyax is not a new chemical entity. It pairs two Lilly drugs, Prozac and Zyprexa, in one pill.

By combining the two drugs in one, "there's a synergy effect beyond what you expect" from taking the two drugs separately, said Dr. Robert Baker, associate medical director for U.S. neurosciences at Lilly.

Baker said Lilly studies show Symbyax is effective in easing the symptoms of depression in bipolar patients without pushing them into mania, which often happens when antidepressants alone are given.

Zyprexa, Lilly's current best-seller, is approved for schizophrenia and acute mania in bipolar disorder. Prozac, Lilly's previous No. 1 drug, is an antidepressant.