It is the responsibility of the patent applicant(s) to disclose in sufficient detail the knowledge a person skilled in the art of the invention to make the invention.
Are you claiming that drug patents should not be allowed because the patent disclosures are inherently insufficient?
I don’t know all the legal ins and outs, only that as a layperson...I can’t just base my judgment on a product on the active ingredient. Through trial and error, I am able to differentiate my body’s responses to various brandname/generic versions of the ‘same’ product even if I can’t pinpoint just which ‘inactive’ ingredient(s) is the source of the varied response. (If any.)
The same goes for non-medicinal things too I suppose. Like preferring a supermarket brand of a food item as opposed to the name-brand.