This is especially true with drugs that are available only by prescription in the United States but sold over the counter in Mexico. And here is a key point: A prescription from a Mexican doctor is no longer acceptable. You may do so if you have a serious medical condition, there are no effective treatments available in the U. The Canadian International Pharmacy Assn. Please note that the rules often change without notice, so it’s important to stay informed. Read below for sites that can help with that. Examples of common medications in the controlled substance list are Oxycontin , Tylenol with Codeine , and Cipro.You can bring prescription medications approved by the Food and Drug Administration (FDA) from Mexico into the United States. But there are limits. The U.S. Customs and Border Protection (CBP) will generally prohibit a supply for more than 90 days to come across the border. Examples of Viagra’s more commonly reported side effects include: headache. flushing (temporary warmth, redness, or deepening of skin color) stuffy nose. indigestion (upset stomach) mild vision.  · You’ll likely start with a Viagra dose of 50 mg. You’ll typically take Viagra about 1 hour before sex. You can take the drug 30 minutes to 4 hours before you anticipate sexual activity.