I hesitate to post this here, because I basically agree with the other posters that you need to be monitored by a Dr. if taking certain prescription medication. But many full timers take advantage of Mexican pharmacies, where it is possible to buy many of these prescription medications over the counter. As one example, Los Algadones, in Mexico, has a 3 or 4 block stretch next to the border crossing full of pharmacies, dentists, and eyeglass places which cater to the hordes of Yanqui tourists who cross over specifically to get medicine or to have dental work done.
https://www.dayodental.com/what-are-the-rules-on-buying-prescription-meds-from-mexico/