Medicines that you take by mouth are called oral medicines. Your doctor or other health care professional can recommend one for you based on these factors, other health conditions you have and any other medicines you take. It works by blocking the molecule that normally gets rid of an erection. Cialis tadalafil is a longer-lasting PDE-5 inhibitor will allow males to achieve erections up to 36 hours after a dose. These medicines all work well for ED. These small differences affect the way each medication works, such as how quickly it takes effect and wears off, and the possible side effects.Drug Images What is Viagra? If you have erectile dysfunction (ED), your doctor may recommend that you take Viagra. It’s a prescription drug that’s used in adult males* with . 25 milligrams (mg) 50 mg mg Typical dosages The following information describes commonly recommended dosages for ED. However, be sure to take the dosage your . 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 women (Revatio .