Statistically speaking, psychiatrists are usually the lowest MCAT scorers so they aren’t really the brightest of drug prescribing doctors. Also, I hope Major isn’t including psychologists with psychiatrists (one can prescribe drugs & the other can’t), and that he realizes that alcohol’s far worse than just taking some serotonin (which I think might not work in Lockem’s case).
There is a possibility that the psychiatrist missed something in which another specialist can identify & treat. Sometimes a pathologist specializing in molecular genetics can help (medical genetics maybe).