What About Medicines?
You can buy a lot of different medicines in Meso-America without a prescription. You probably won't find anything fancy, but generics are abundant. I have never been even questioned about taking antibiotics or asthma meds back home, but if you take serious controlled substances, you would do well to either have a prescription or leave them behind when you return home.
The prices you will find will be better than you find in many places, particularly if you live in the US. It is a good idea to look at the expiration date on what you are buying, because they should be shown.
It is a good idea to buy some Ciprofloxacin on arrival in case of serious intestinal problems. The same goes for Chloroquine, but you are supposed to start that a week before heading into a malarial area.
For medical travel information, see Travmed.com