Flibanserin is not approved in Australia. If you experience chest pain, dizziness, or nausea during sex, seek immediate medical help. Grapefruit juice: Grapefruit juice can increase the amount of Viagra Sildenafil in your bloodstream. Liver function: If you have poor liver function you may need lower doses of Viagra Sildenafil. Taking sildenafil alone will not cause an erection.Sildenafil (Viagra) is a medicine used to treat erectile dysfunction (ED, also called impotence). Sildenafil works by helping to relax the blood vessels in the penis, allowing more blood to flow in and cause an erection. You should take sildenafil about an hour before planned sexual activity, so it has time to work. Sildenafil (Viagra) is used to treat erectile dysfunction (impotence; inability to get or keep an erection) in men. Sildenafil (Liqrev, Revatio) is used to improve the ability to exercise in adults (Liqrev, Revatio) and children 1 year of age and older (Revatio) with pulmonary arterial hypertension (PAH; high blood pressure in the vessels carrying blood to the . Over Products Tested · Honest & Unbiased Reviews · Top Brands Voted By Men.