As a psychopharmacologist, I can tell you straight up that this would be the absolute stupidest way to dispense medication that I have ever heard of, and I have heard of plenty. There is NOT ONE medication that everyone needs to be on, there would be absolutely no control over dosages, there would have to be numerous other chemicals added for use as carrying agents for the thousands of drugs that are not water soluble, physicians would be prevented from ever making a truly confident diagnosis, and so on and on (I could list probably hundreds of other reasons).
Pharmacology is very complicated and highly individualized. I work in the field and the complexities can be so overwhelming as to be incomprehensible, so to an average "layperson", this is something far beyond what even a Bachelor's Degree's worth of Bio/Chem would provide. I do NOT in any way mean that in a negative/disrespectful way, so please understand that and don't flame me. This simply happens to be my field.