All medications must be declared upon arrival at the border. 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. Of course, many drugs that require a prescription in the US are sold over the counter here. However, if you have medications that are considered a controlled substance including some cough medicines, tranquilizers, sleeping pills, antidepressants, or stimulants, you may only bring up to 50 dosage units across the border without a prescription. You will also need to provide the name and address of the U. That’s especially true if you want to purchase name brands.Almost the same with Viagra. So, yes it is available without any script, but the prices do not match up with Chicago and going the normal way of getting the stuff. Now, if you have to . Cancun, Mexico. Level Contributor. 3, posts. 6. Re: Over the Counter Drugs. 12 years ago. Save. In April my DH tried to buy some Amoxicillin to bring back with no luck at . Answer 1 of 9: I have a question. Simple Can you buy drugs at a drug store in Cancun over the counter that you can’t buy in the US without a prescriptio? Example. Viagra. .