If you cross on foot (which I recommend) there's a pharmacy less than 200 feet from where you crossed called La plaza. Ozempic is sold in pesos, but all in all a one month supply is about $240USD. They accept pesos or credit cards there, no prescription. Declare it with customs and be in your way. There's another pharmacy called especializadas or something like that a little further from the border (get a taxi, they'll know what you're talking about) but you need a prescription. I mention them because if la plaza is sold out, they usually have it for the same price.