In the USA its a strict legal requirement that you 1) can always choose which pharmacy you want your prescription sent to (doesn’t mean that they accept your insurance tho) and 2) your prescriber MUST send your prescription there barring a weird exception like they suspect a crime or self harm
I know... It's ridiculous. I don't want that. I want the doctor to give me the prescription and I want to use it anywhere I so desire. My doctor doesn't care and doesn't need to know where I want to buy the medication.
So who will start the medstr? The doctor signs and marks the patient.