Which makes sense, if you remember that there used to not be such a thing as pre-compounded drugs. Rather, a prescription was literally a recipe a doctor would write out for you to give to your friendly neighbourhood compounding pharmacist, who would follow that recipe to produce a drug for you.

Which in turn lends an interesting clarity to the traditional roles and competencies of "medical doctors" vs "pharmacists". In the 1800s, a trained doctor was someone who would be expected to come up with a — potentially de-novo! — drug formulation, on the spot, as a treatment for a patient; and a trained pharmacist is someone who would be expected to take your prescription, walk into a lab in the back of their shop, and come out having converted that — potentially never-before-encountered — drug formulation into something you could put in your mouth. If the active ingredient was something unusual, they would even be expected to synthesize it themselves! (Which explains why we used to call pharmacists "chemists". They were!)