This topic comes up on all the boards from time to time. My understanding is that the letter of Mexican law requires a Rx from a Mexican physician to buy Vigara, Cialis and Levitra (V/C/L) as they are category four prescription medications.
(Cialis's registration number, for example, is 181M2002 SSA IV.) Granted the law is seldom enforced (unless one is a tourist) and that even pharmacists will tell you a Rx isn't needed. (Which is partly true: they don't need a Rx to sell V/C/L to you.)
Below is part of my post in the FAQ forum on TJ Amigos. I hope it answers the question, but doubt it will.
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I have heard many people debate the question whether an Rx is need to buy medication in Mexico. The Mexican government provides the following on-line information that all (who speak Spanish) can review.
http://www.salud.gob.mx/unidades/cdi/nom/072ssa13.html
NORMA Oficial Mexicana NOM-072-SSA1-1993, Etiquetado de medicamentos.
5.11.1 En la etiqueta de los medicamentos, se deberู expresar la clave de registro sanitario, tal como se indica en el oficio de registro, seguida del nูmero romano de la fracciูn que corresponda a los medicamentos, ambos con la misma tipografูa y tamaูo, y de acuerdo a la siguiente clasificaciูn:
I. Medicamentos que sูlo pueden adquirirse con receta o permiso especial, expedido por la Secretarูa de Salud;
II. Medicamentos que requieren para su adquisiciูn receta mรฉdica que deberู retenerse en la farmacia que la surta y ser registrada en los libros de control que al efecto se lleven;
III. Medicamentos que sูlo puedan adquirirse con receta mรฉdica que se podrู surtir hasta tres veces;
IV. Medicamentos que para adquirirse requieren receta mรฉdica, pero que pueden resurtirse tantas veces como lo indique el mรฉdico que lo prescriba;
V. Medicamentos sin receta, autorizados para su venta exclusivamente en farmacias, y
VI. Medicamentos que para adquirirse no requieren receta mรฉdica y que puedan expenderse en otros establecimientos que no sean farmacias.
Medications fall into one of several categories (or schedules):
Category I medications may only be taken with permission of the Secretary of Health. Usually they are experimental drugs.
Category II drugs require the pharmacy to keep records on who bought the medication. They will probably keep your Rx and you will need a new Rx each time you visit the pharmacy.
Category III medications are limited to three refills. Obviously records should be kept by the pharmacy.
Category IV medications require an Rx from a Mexican physician. However, the pharmacy is not required to keep records about who bought the medication.
Category V medications do not require an Rx. They can only be sold in a pharmacy.
Category VI medications do not require an Rx. Their sale in not restricted to a pharmacy (think of something like Aspirin sold in grocery stores).
In many Latin American countries so many people lack money to visit physicians that pharmacists often provide medical care. Hence laws requiring a person to have an Rx are seldom enforced. The pharmacy may even tell you that you don't need an Rx for Category IV--> medication. However, the law is on the books and an "enterprising cop" can use it to extort money. (Fortunately, this seldom happens.)
Most prescription medications--including Viagra, Cialis, and Levitra--are Category IV medication. (Cialis's registration number, for example, is 181M2002 SSA IV.) The regulation above says these medications require a prescription from a Mexican physician and that it can be refilled as many times as the doctor indicates. Since record keeping by the pharmacy is not required for Category IV medications many people and pharmacies say an Rx is not required. While this is correct in practice, it is not correct legally.
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My TJ Amigos post includes the name and address of a Mexican physician who wrote me a Rx for Levitra. He charged me $30.00.
In many places I've given this advice: If you are going to buy V/C/L without a Rx keep an eye out for cops. It is best to use a pharmacy that isn't near the Zona or Revolucion. When buying V/C/L also buy a Coke. Take the tablet before leaving the pharmacy. (Leave the box behind.) If you are spotted leaving the pharmacy you can claim you just bought a Coke.