For antibiotics specifically, many manufacturers will sell them "for fish use". This will have an identical manufacturing process, but won't follow the guidelin

For antibiotics specifically, many manufacturers will sell them "for fish use". This will have an identical manufacturing process, but won't follow the guidelines for packaging, storing, and shipping antibiotics. So a bit more risk, but no prescription needed and significantly cheaper. Alternatively, Indian mail-order pharmacies will successfully ship most things to the US in a plain brown envelope. It's technically illegal, but there's approximately zero enforcement action against it, the most they'll do is seize the shipment. Painkillers, opioids, amphetamines, and other pharmaceuticals with abuse risk are probably not going to be available this way (or advisable), but everything without a significant abuse risk has pretty much zero arrests.