The four main medicines taken by mouth for erectile dysfunction are: Avanafil (Stendra). Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called .Often, these are prescribed for chest pain called angina. Typically this takes the form of a tick box medical questionnaire, which is then reviewed by the pharmacist prior to supply. This medicine also works best when you take it an hour before sex on an empty stomach. Your doctor will tell you not to take sildenafil if you are taking street drugs containing nitrates. Best for. This increased blood flow can cause an erection. If you are taking sildenafil to treat PAH, you will probably take sildenafil three times a day with or without food.1. How it works. Sildenafil may be used to treat erectile dysfunction (ED or impotence) in men (Viagra brand) or pulmonary arterial hypertension in both men and . 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 . The four main medicines taken by mouth for erectile dysfunction are: Avanafil (Stendra). Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called .Before starting, stopping, or changing any medications while taking sildenafil, please get the advice of your doctor or pharmacist. The Korean Court system made a ruling against Pfizer in June , allowing for the unhindered domestic production of generic prescription sildenafil. On 6 May , Pfizer , which manufactures Viagra, told the Associated Press they will begin selling the drug directly to people on its site. A prescription from your GP may allow you to get Viagra or unbranded Sildenafil for a lower cost than over-the-counter Viagra Connect. The decision, Teva Canada Ltd.