The body takes longer to absorb it after a high-fat meal or alcohol. Its effects often last for 4 to 5 hours. These include itraconazole Sporanox, Tolsura , ketoconazole Extina, Ketozole, others and ritonavir Norvir. Some examples of nitrates are nitroglycerin Nitro-Dur, Nitrostat, others , isosorbide mononitrate Monoket and isosorbide dinitrate Bidil. A newer form of the medicine that dissolves on the tongue might work faster than the pill that you swallow. The most common side effects of VIAGRA: headache; flushing; upset stomach; abnormal vision, such as changes in color vision such as having a blue color tinge and blurred vision; stuffy or runny nose; back pain; muscle pain; nausea; dizziness; rash. Oral medicine for ED also might not be safe or work well if you have: Very low blood pressure, called hypotension, or uncontrolled high blood pressure, called hypertension.The four main medicines taken by mouth for erectile dysfunction are: Avanafil (Stendra). Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called . 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. What we found in counterfeit VIAGRA: Blue printer ink; Amphetamines, also known as “speed” Metronidazole, a powerful antibiotic that could cause an allergic reaction, .