The present invention is directed to pharmaceutical formulations containing 6-hydroxy-3-(4-[2-(piperidin-1-yl)ethoxy]phenoxy)-2-(4-methoxypheny)benzo- [b]thiophene or a salt thereof; stabilized to oxidation or other forms of decomposition by incorporation of a stabilizing agent selected from methionine, acetylcysteine, cysteine or salts thereof.