But any doctor can do it, not just SUS doctors. You know the country we live in. Private doctors will do the prescription... Actually, to buy it you already need a prescription, and yet, even skinny healthy folks buy ozempic.
And to get in the SUS, it's pretty simple here in Paraná at least (and as a SUS user). The worst that happens, it's that for expensive/controlled medicines, they centralize into a single public pharmacy in the city center, and you need to schedule a day/time, and bring the ID - don't even need to be the user, you can ask anyone you want to get it if the prescription and ID it's there.
Which is why for my cheap medicine, I prefer to buy it. Not worth for me going to city center only for 30 pills that cost R$ 15.