1. About sildenafil
Sildenafil is a medicine used to treat erectile dysfunction. It increases blood flow to the penis to help men get an erection. At least two-thirds of men have improved erections after taking it.
Sildenafil is also sometimes used to treat pulmonary hypertension (high blood pressure in the blood vessels that supply the lungs).
This medicine is available on prescription and can also be bought from most pharmacies. It comes as tablets that you swallow, chewable tablets, and as a liquid that you drink.
2. Key facts
It usually takes 30 to 60 minutes for sildenafil to work for erectile dysfunction. You can take it up to 4 hours before you want to have sex.
Taking sildenafil alone will not cause an erection. You need to be aroused for it to work.
The most common side effects are headaches, feeling sick, hot flushes and dizziness. Many men have no side effects or only mild ones.
It can be dangerous to take sildenafil if you also take medicines called nitrates (often given for chest pain). The combination can cause a dangerous fall in your blood pressure. If you're not sure if you're taking a nitrate, ask your doctor or pharmacist.
Sildenafil is called by the brand names Viagra (for erectile dysfunction) and Revatio (for pulmonary hypertension).
3. Who can and can't take sildenafil
Sildenafil for erectile dysfunction (Viagra) can be taken by men aged 18 and over. It's not for women or children.
Sildenafil for pulmonary hypertension (Revatio) can be taken by adults and children aged 1 and over.
Sildenafil is not suitable for some people.
Do not take sildenafil if you:
have had an allergic reaction to sildenafil (Viagra) or any other medicines in the past
are taking medicines called nitrates for chest pain
have a serious heart or liver problem
have recently had a stroke or a heart attack
have low blood pressure
have a rare inherited eye disease, such as retinitis pigmentosa
