Sildenafil (Viagra)
NHS information about the medicine sildenafil, including what it's used for, who can use it, how to use it and side effects.
What sildenafil is for
Sildenafil is mainly used to treat erection problems (erectile dysfunction).
It's also used to treat pulmonary arterial hypertension.
How to take sildenafil
Sildenafil usually comes as tablets or a liquid that you swallow.
How much you need to take and how long for depends on why you're taking it. If a doctor has prescribed it, they will tell you how much to take and how often.
Always check the packet or leaflet that comes with your medicine. Ask a pharmacist or doctor for advice if you're not sure how to take it or have any problems taking it.
People with erection problems are usually told to take 1 tablet 1 hour before sex, but the amount of time it takes to work can vary. Do not take more than 1 tablet a day as the effects can last up to 36 hours.
Swallow the tablet whole with some water.
Side effects of sildenafil
Like all medicines, sildenafil can cause side effects, but not everyone gets them.
Common side effects
Common side effects of sildenafil can include:
- headache
- dizziness
- blocked or stuffy nose
- stomach ache, diarrhoea or feeling sick (nausea)
- anxiety
- temporary changes in vision, such as blurred vision
If you feel dizzy or have blurred vision after taking sildenafil, do not drive, ride a bike or use machinery until you no longer have these symptoms.
More about side effects
These are not all the side effects of sildenafil.
For a full list, see the leaflet that came with your medicine or search for your medicine leaflet on the electronic medicines compendium website.
You can report any side effects you get on the Yellow Card website.
Who can and cannot take sildenafil
Most adults can take sildenafil.
But sildenafil is not suitable for everyone. For example, it may not be suitable if:
- you've ever had an allergic reaction or serious side effect from sildenafil
- you've recently had a heart attack or stroke
- you have low blood pressure or uncontrolled high blood pressure
- you have liver or kidney problems
- you have blood cancer (leukaemia) or cancer of the bone marrow (multiple myeloma)
- you have sickle cell anaemia
- you've ever had vision loss caused by reduced blood flow to the optic nerve (non-arteritic anterior ischemic optic neuropathy)
- you have a curved or bent penis, which makes getting an erection painful or difficult
Before taking sildenafil, tell your doctor if you have any medical conditions.
Breastfeeding and sildenafil
Tell your doctor if you're breastfeeding. Sildenafil is not usually used while breastfeeding. You doctor may offer a different treatment.
Pregnancy and sildenafil
Tell your doctor if you're pregnant or trying to get pregnant. Sildenafil is not usually used during pregnancy, but your doctor my recommend it if the benefits outweigh the risks.
Taking sildenafil with other medicines, food and drink
There are some medicines and supplements that may not mix well with sildenafil.
This includes some types of:
- heart medicines, such as nitrates for chest pain (angina)
- epilepsy medicine (anticonvulsants)
- medicine for pulmonary hypertension or high blood pressure
- antibiotics, including rifampicin, erythromycin and clarithromycin
- medicine for enlarged prostate or erectile dysfunction
- medicine for HIV or AIDS
- antifungal medicines
- supplements containing St John's Wort
Taking sildenafil together with poppers (amyl nitrate) or illegal drugs, such as amphetamines, ecstasy and cocaine, can increase the risk of serious side effects.
This is not the full list of medicines that may not mix well with sildenafil. Before taking it, tell your doctor if you’re taking any other medicines, herbal remedies, vitamins or supplements.
Food, drink and alcohol with sildenafil
You can generally eat as normal while taking sildenafil, but do not eat grapefruit or drink grapefruit juice because it can make it more likely you'll get side effects.
You may find it takes longer to get an erection if you take it after eating a large meal.
It's best to avoid drinking too much alcohol when taking sildenafil because it can make getting an erection more difficult.
Find out more about your medicine
To find out more about your medicine, you can:
- check the leaflet that comes with it
- search for your medicine leaflet on the electronic medicines compendium website
- speak to a pharmacist or doctor for advice
