Sexual activity may be a strain on your heart, especially if you have heart disease. Please note that the rules often change without notice, so it’s important to stay informed. Do not mix the liquid with other medications or add anything to flavor the medication. These medicines are called PDE5 inhibitors. Required Documentation Mexican pharmacies offer prescription medications at lower prices than pharmacies in the United States. But there are limits.More From Men’s Health. Eroxon, the brand name for MED, is currently available in Belgium and the U.K. It claims to “help you get an erection within 10 minutes.”. About . The average length of time Viagra lasts. On average, Viagra lasts between 2 and 3 hours before its effects start to diminish. Viagra can last up to 5 hours or longer depending on your dosage, your. Imported drugs from a Mexican pharmacy can carry some serious risks. The FDA is only responsible for drugs marketed and sold in the U.S., so there is no guarantee or monitoring of drug purity, safety, or quality. This is especially true with drugs that are available only by prescription in the United States but sold over the counter in Mexico.