Without physical action to the penis, such as that occurring during sexual intercourse, sildenafil will not work to cause an erection. Who may not be able to take sildenafil Sildenafil is not suitable for some people. Rarely reported side effects include: an erection that will not go away priapism. If you have an erection that lasts more than 4 hours, get medical help right away. You can take this medicine with or without food 30 minutes before sex, depending on the dose. Erectile dysfunction is a condition where the penis does not harden and expand when a man is sexually excited, or when he cannot keep an erection. This product is available in the following dosage forms: Tablet Suspension There is a problem with information submitted for this request.La mayoría de los efectos secundarios del Viagra se presentan en muy pocos casos y son leves, tales como: Enrojecimiento de la cara. Sensación de calor. Dolor de cabeza. Diarrea. Dolores articulares o musculares, calambres. Adormecimiento de brazos y piernas. Trastornos del sueño. Congestión o sangrado nasal.  · a light-headed feeling, like you might pass out. Common sildenafil side effects may include: flushing (warmth, redness, or tingly feeling); headache, dizziness; heartburn, nausea, or upset stomach. abnormal vision (blurred vision, changes in color vision) runny or stuffy nose, nosebleeds; sleep problems (insomnia); or.  · VIAGRA is supplied as blue, film-coated, rounded-diamond-shaped tablets containing sildenafil citrate equivalent to 25 mg, 50 mg, or mg of sildenafil. Tablets are debossed with PFIZER on one side and VGR25, VGR50 or VGR on the other to indicate the dosage strengths. 4. Contraindications.