Customs officials will generally want a letter from the individual patient stating that the drug from a Mexican pharmacy is intended for personal use to treat a serious medical condition. While on an outing in Tijuana last year, she popped into a few pharmacies to see if they stocked her medications. A couple of sites do the vetting for you, using these and other criteria. You must have one from a Mexican doctor to but drugs that are prescription here. It does, however, give law-abiding Americans some options if they can’t get or can’t afford medications in the U. For example, you will be limited to a three-month supply.First: It is technically illegal. Second: It is unlikely you will be prosecuted. Despite the official prohibition, FDA guidelines allow federal agents to refrain from enforcement “when the. Can I buy generic Viagra over the counter or do I need a prescription? In the U.S. and most other countries, generic Viagra is only available with a prescription. The U.S. has the highest prescription drug costs in the world, prompting many people to seek savings by buying their medicines from Canadian or Mexican pharmacies. But if .