What is sildenafil?
Sildenafil relaxes muscles of the blood vessels and increases blood flow to particular areas of the body.
Sildenafil under the name Viagra is used to treat erectile dysfunction (impotence) in men.
Another brand of sildenafil is Revatio, which is used to treat pulmonary arterial hypertension and improve exercise capacity in men and women.
Do not take Viagra while also taking Revatio.
Do not take sildenafil if you are also using a nitrate drug for chest pain or heart problems, including nitroglycerin, isosorbide dinitrate, isosorbide mononitrate, and some recreational drugs such as “poppers”. Taking this drug with a nitrate medicine can cause a sudden and serious decrease in blood pressure.
Some medicines can cause unwanted or dangerous effects when used with this drug. Tell your doctor about all your current medicines, especially riociguat (Adempas). Do not take sildenafil with riociguat.
Contact your doctor or seek emergency medical attention if your erection is painful or lasts longer than 4 hours. A prolonged erection (priapism) can damage the penis.
Stop using sildenafil and get emergency medical help if you have sudden vision loss.
Before taking this medicine
You should not use sildenafil if you are allergic to it, or:
- if you take other medicines to treat pulmonary arterial hypertension, such as riociguat (Adempas).
Do not take this medicine if you are also using a nitrate drug for chest pain or heart problems. This includes nitroglycerin, isosorbide dinitrate, and isosorbide mononitrate. Nitrates are also found in some recreational drugs such as amyl nitrate or nitrite (“poppers”). Taking this drug with a nitrate medicine can cause a sudden and serious decrease in blood pressure.
To make sure sildenafil is safe for you, tell your doctor if you have ever had:
- heart problems (chest pain, a heart rhythm disorder, heart attack);
- high or low blood pressure;
- blood circulation problems;
- retinitis pigmentosa (an inherited condition of the eye);
- blindness in one or both eyes;
- bleeding problems;
- a stomach ulcer;
- pulmonary veno-occlusive disease (PVOD);
- liver or kidney disease;
- a blood cell disorder such as sickle cell anemia, multiple myeloma, or leukemia;
- a physical deformity of the penis (such as Peyronie’s disease); or
- if you have been told you should not have sexual intercourse for health reasons.
Sildenafil can decrease blood flow to the optic nerve of the eye, causing sudden vision loss. This has occurred in a small number of people taking sildenafil, most of whom also had heart disease, diabetes, high blood pressure, high cholesterol, or certain pre-existing eye problems, and in those who smoked or were over 50 years old. It is not clear whether this medicine is the actual cause of vision loss.
This medicine is not expected to harm an unborn baby. Tell your doctor if you are pregnant or plan to become pregnant. Women with pulmonary arterial hypertension should not stop taking sildenafil without talking to their doctor.
It is not known whether sildenafil passes into breast milk or if it could harm a nursing baby. Tell your doctor if you are breast-feeding a baby. Women with pulmonary arterial hypertension should not stop taking sildenafil without talking to their doctor.
Do not give this medication to anyone under 18 years old without medical advice.
How should I take this drug?
Take sildenafil exactly as it was prescribed for you. Follow all directions on your prescription label and read all medication guides or instruction sheets.
Revatio is usually taken three times each day, about 4 to 6 hours apart.
Viagra is usually taken only when needed, 30 minutes to 1 hour before sexual activity. You may take it up to 4 hours before sexual activity. Do not take Viagra more than once per day.
Shake the oral suspension (liquid) before you measure a dose. Use the dosing syringe provided, or use a medicine dose-measuring device (not a kitchen spoon).
Viagra can help you have an erection when sexual stimulation occurs. An erection will not occur just by taking a pill. Follow your doctor’s instructions.
During sexual activity, if you become dizzy or nauseated, or have pain, numbness, or tingling in your chest, arms, neck, or jaw, stop and call your doctor right away. You could be having a serious side effect of sildenafil.
Store at room temperature away from moisture and heat.
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 this drug 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 this drug 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
Check with your doctor before taking sildenafil if you:
- have sickle cell anaemia (an abnormality of red blood cells), leukaemia (cancer of blood cells) or multiple myeloma (cancer of bone marrow)
- have a deformity of your penis or Peyronie’s disease (curved penis)
- have a heart problem. Your doctor should carefully check whether your heart can take the additional strain of having sex.
- have a stomach ulcer or a bleeding problem like haemophilia
4. Where to get sildenafil
On the NHS
You can get sildenafil on the NHS if you have erectile dysfunction or pulmonary hypertension.
Branded versions of sildenafil such as Viagra are not available on the NHS, except in special circumstances.
You can also get sildenafil on a private prescription from your doctor. This means you’ll need to pay the full cost of the medicine.
Prices vary, but on average 4 tablets costs around £20.
From a pharmacy
You can buy sildenafil from a pharmacy following a discussion with the pharmacist.
They’ll ask you some questions about your general health to make sure this drug is safe for you to take. You can also talk to them about side effects.
If the pharmacist has any concerns about whether this drug is safe for you, they may advise you to see your doctor.
You can buy this drug/Viagra over the internet. Be very careful if you do this as many websites sell fake medicines.
Online medicines are not always regulated and the ingredients in them can vary from one pack to another. They can cause unpleasant side effects or may not be suitable for you.
It’s best to see your doctor before buying medicines online. They know your medical history and can discuss whether you might benefit from treatment.
If you choose to buy this drug/Viagra over the internet, make sure:
5. How and when to take it
It’s important to take it as advised by your doctor or pharmacist.
How much will I take for erectile dysfunction?
Sildenafil tablets for erectile dysfunction come in different strengths ranging from 25mg to 100mg.
The usual dose is 50mg, when you need it (no more than once a day).
The dose can be increased to 100mg or decreased to 25mg depending on its effect.
Take sildenafil up to 4 hours before you want to have sex. For sildenafil to work properly, you’ll need to be sexually excited.
How much will I take for pulmonary hypertension?
Sildenafil tablets for pulmonary hypertension come in 10mg and 20mg tablets.
The usual adult dose is 20mg taken 3 times a day.
Doses for children can range from 10mg to 20mg taken 3 times a day, depending on their weight.
How to take it
Swallow tablets whole with a glass of water or juice (but not grapefruit juice).
For erectile dysfunction, it’s best to take sildenafil on an empty stomach. It may take longer to work if you take it with food.
If you or your child are taking sildenafil as a liquid, 1ml is usually the same as taking a 10mg tablet, but it’s important to always check the medicine label.
Liquid sildenafil will usually be made up for you by your pharmacist.
The medicine will come with a plastic syringe or spoon to help you take the right amount.
If you do not have a plastic syringe or spoon, ask your pharmacist for one. Do not use a kitchen teaspoon as it will not give the right amount.
What if I forget to take it?
If you have pulmonary hypertension and you forget to take a dose of sildenafil, take it as soon as you remember and then continue as usual.
Never take 2 doses at the same time. Never take an extra dose to make up for a forgotten one.
If you often forget doses, it may help to set an alarm to remind you.
You could also ask your pharmacist for advice on other ways to help you remember to take your medicine.
What if I take too much?
Taking too much sildenafil by accident can cause unpleasant side effects, such as:
- blocked nose
- altered vision
Talk to your doctor if you have taken too much sildenafil and you’re worried about these side effects.
6. Side effects
Like all medicines, sildenafil can cause side effects in some people. Many people have no side effects or only minor ones.
Common side effects
Common side effects happen in more than 1 in 100 people.
If you get these side effects, keep taking the medicine, but tell your doctor or pharmacist if these side effects bother you or do not go away:
- feeling sick
- hot flushes, including facial flushing
- a colour tinge to your vision or blurred vision
- stuffy nose
Serious side effects
Serious side effects are rare and happen in less than 1 in 1,000 people.
Stop taking sildenafil and call a doctor straight away if you get:
- chest pains – if this happens during or after sex, get into a semi-sitting position and try to relax; do not use nitrates to treat your chest pain
- prolonged and sometimes painful erections – if you have an erection that lasts for more than 4 hours, contact a doctor immediately
- a sudden decrease or loss of vision
- a serious skin reaction – symptoms may include fever, severe peeling and swelling of the skin, blistering of the mouth, genitals and around the eyes
If someone has overdosed and has serious symptoms such as passing out or trouble breathing, call 911. Otherwise, call a poison control center right away. US residents can call their local poison control center at 1-800-222-1222. Canada residents can call a provincial poison control center. Symptoms of overdose may include severe dizziness, fainting, painful/prolonged erection.
Do not share this medication with others.
Store at room temperature away from light and moisture. Do not store in the bathroom. Keep all medications away from children and pets.
Do not flush medications down the toilet or pour them into a drain unless instructed to do so. Properly discard this product when it is expired or no longer needed. Consult your pharmacist or local waste disposal company.Information last revised February 2019