Reb Yidd:
Come on. The prescribing physician (whether psychiatrist or other) needs to prescribe the best medication for the condition, considering the specific needs of the patient. A generalization that has close to 100% accuracy, is that medications (of any kind) and alcohol don’t mix. Either there is the blocking of the effect, the synergy effect, or other interactions that can vary from the ho-hum to the fatal. One can always fulfill obligations for kiddush etc. with grape juice, or to be yotzeh with someone else. I would not limit a doctor’s ability to prescribe to preserve the option of drinking, especially heavy drinking. That constitutes severe confusion between an ikar and a tofel.
The poskim address the situation of the individual who cannot drink safely. This includes someone on meds, and also includes someone recovering from alcohol or drug addiction. Pikuach nefesh is not overridden by Purim. The entire holiday of Purim is about the preservation of life, that Haman wanted to exterminate all of Klal Yisroel, and that we were zocheh to be saved. To “celebrate” with risk to life is antithetical to the entire holiday.