Rarely reported side effects include: an erection that will not go away priapism. These medicines all work well for ED. Avanafil Stendra. The four main medicines taken by mouth for erectile dysfunction are: Avanafil Stendra. When choosing one, tell your doctor or other health care professional what your preferences are, such as cost, ease of use, how long the drug’s effects last and side effects.Viagra isn’t Pfizer’s only counterfeit headache: in , according to John Clark, vice president of global security for the company, about 20 different Pfizer . What we found in counterfeit VIAGRA: Blue printer ink; Amphetamines, also known as “speed” Metronidazole, a powerful antibiotic that could cause an allergic reaction, . Viagra, which in the past advertised heavily on TV, but no longer does, is a well-known prescription medicine for erectile dysfunction (ED). It also has the distinction of being one of the most counterfeited drugs in the world, says its marketer, Viatris, which estimates that 30 million men in the U.S. suffer from ED. AARP Membership.