What is a yellow Xanax? Pill with imprint S 901 is Yellow, Elliptical / Oval and has been identified as Alprazolam 0.5 mg. It is supplied by Dava Pharmaceuticals Inc.. Alprazolam is used in the treatment of anxiety; panic disorder and belongs to the drug class benzodiazepines. Xanax is taken by mouth and is readily absorbed into the bloodstream. You should start feeling the effects of Xanax in...