These include itraconazole Sporanox, Tolsura , ketoconazole Extina, Ketozole, others and ritonavir Norvir. If you prefer, you may contact the U. You are encouraged to report adverse events related to Viatris products by calling U. Data shared with Viatris will be aggregated and de-identified; it will be combined with data related to other Savings Offer redemptions and will not identify you Viatris reserves the right to rescind, revoke, or amend this Savings Offer without notice No membership fees. The four main medicines taken by mouth for erectile dysfunction are: Avanafil Stendra. As with sildenafil, a high-fat meal or alcohol keep the body from absorbing it as quickly.Sildenafil (Viagra). This medicine works best when you take it on an empty stomach an hour before sex. The body takes longer to absorb it after a high-fat meal or alcohol. Its effects often last for 4 to 5 hours. It might work longer if you have mild to moderate erectile dysfunction. Vardenafil. Viagra (sildenafil) is a phosphodiesterase-5 (PDE5) inhibitor used for the treatment of erectile dysfunction. What Are Side Effects of Viagra? Side effects of Viagra include: warmth or redness in the face, neck, or chest, stuffy nose, headaches, stomach pain, upset stomach, nausea, diarrhea, memory problems, back pain. Side Effects. Dizziness, headache, flushing, or stomach upset may occur. Vision changes such as increased sensitivity to light, blurred vision, or trouble telling blue and green colors apart may.