Sildenafil is a medication used to treat erectile dysfunction and pulmonary arterial hypertension. Sildenafil blocks the enzyme (phosphodiesterase 5) that promotes breakdown cGMP (Cyclic guanosine monophosphate) which regulates blood flow in the spongy tissue of the penis, causing an erection. The effect requires sexual arousal. The half life is 4-5 hours.
Common side effects include headache, heartburn, flushed skin, vision problems, hearing loss, low blood pressure, heart attack, ventricular arrhytmias, stroke, prolonged erections and penis damage.
The recommended dose is 25-100mg once a day, up to 4 hour before sexual activity. Sildenafil starts to work within 30-60 minutes. Sildenafil works best on an empty stomach.