Instead of being used daily, Viagra should only be used as necessary. Sildenafil is in a class of medications called phosphodiesterase PDE inhibitors. Erectile dysfunction can often be traced to the same causes as cardiovascular disease, including inflammation, a narrowing of the arteries, or a hardening of the arteries. He instructed the pharmacist to bag the available bottles they have of controlled drugs, or else he would shoot the person closest to him. Ask your healthcare professional how you should dispose of any medicine you do not use. When hypertension occurs in the lungs, the heart must work harder to pump enough blood through the lungs.Strengths: 25 mg, 50 mg, mg; Brand: Viagra. Form: oral tablet; Strengths: 25 mg, 50 mg, mg; Adult dosage (ages 18–64 years) Typical dosage: 50 mg, taken as needed about 1 hour before.  · Print Save Sildenafil Dosage Medically reviewed by test1.ru Last updated on Applies to the following strengths: 10 mg/mL; 10 mg/ mL; 20 mg; 25 mg; 50 mg; mg Usual Adult Dose for: Erectile Dysfunction Pulmonary Hypertension Usual Geriatric Dose for: Erectile Dysfunction Additional dosage . The effects of taking mg of Viagra can last for up to 4 hours after taking the drug. However, the strength of these effects is weaker at 4 hours than 2 hours after taking Viagra.