Viagra works by increasing blood flow to the penis as sexual stimulation occurs. Since erections are caused and maintained by an increased amount of blood in the member, this increase in penile blood helps to eliminate impotence. Viagra does this by inhibiting relaxing the muscles that control the arteries that bring blood to the area. Medically speaking, it is a phosphodiesterase (PDE) inhibitor. PDE is responsible for the arterial tension that can slow blood flow, so inhibiting it has the opposite effect.

Viagra is made in 25mg, 50mg and 100mg tablets that are taken by mouth. Your doctor will determine which dose is best for you. This medicine is taken on an as-needed basis. Unlike some other erectile dysfunction drugs, it may be taken daily.

Like all drugs, Viagra has the possibility of causing side effects. The most common side effects are: headaches, diarrhoea, congestion, bluish vision, facial flushing, heartburn, urinary tract infections (UTIs), muscle aches, insomnia and sensitivity to light. Rare but serious side effects can include chest pain, blurry vision, loss of vision, dizziness, sudden decrease in hearing, loss of hearing, erections lasting longer than four hours, ringing in ears, faintness, rash and worsening shortness of breath. If you experience any of the serious side effects, you should stop taking Viagra and see a doctor immediately.