Sildenafil side effects: What are the risks of taking viagra?

We all know Viagra. It’s the go-to option for lots of men with erectile dysfunction. As great as it is, it isn’t the ideal treatment for every man in the world. Viagra side effects can and do happen, but fortunately the number of men that experience them is small. 

If you’re thinking of taking Viagra or sildenafil citrate but want to know more about side effects, you’re in the right place. Being aware of the Viagra risks means that you’ll be more in-the-know should they happen.

Viagra has a half-life of up to four hours. This is the time it takes for a drug’s active ingredient to be metabolized and reduced by half in the body. That means that you shouldn’t get any long term side effects from Viagra. When the drug is no longer in your system, any side effects you do get should calm down too (as long as you’ve stuck to the instructions).

If you’re an older man, some side effects are more likely when taking Viagra. In most cases you’ll start on a lower dose to see how you react to the medication. This is usually the safer option, as it lowers the risk of side effects.

What side effects can you get from Viagra?

There’s a (fairly long) list of side effects with the Viagra pill, and this can look overwhelming at first. Viagra is generally considered to be a low-risk medicine, but it’s good to know what the side effects are so you can do something about them if you need to. 

So if you’re wondering what the side effects of sildenafil are, then we’ll get right to it.

Viagra contains the active ingredient sildenafil citrate, which is a PDE5 inhibitor. This group of medications has been linked to side effects that can affect blood pressure.

A slight rise or fall in blood pressure is not usually something to worry about, as long as your blood pressure returns to normal after the drug has worn off (normally after four hours).

Some men with ED may already be taking medicine to lower their blood pressure. If you are, it’s important to tell the prescriber, because these medications can interact with sildenafil.

If you already have low blood pressure, it’s likely sildenafil won’t be safe for you.

Page reviewed by:
Mr Craig Marsh
Mr Craig Marsh
Pharmacist Prescriber
Visit author profile
Last updated August 9, 2021

Common Sildenafil side effects

Common side effects may affect up to 1 in 10 people and include:
  • nausea (feeling sick)
  • facial flushing (where your face turns red)
  • hot flash (a sudden feeling of heat in your upper body)
  • indigestion (this could feel like heartburn or bloating)
  • color change to vision
  • blurred vision
  • visual disturbance
  • stuffy nose
  • dizziness

What to do about a Viagra headache

When you take Viagra or Sildenafil, getting a headache is a very common side effect, which means it affects more than one in 10 men. Viagra and Sildenafil aren’t alone in this — it’s reported a lot with other ED drugs too.

For a lot of men, a headache isn’t much of a problem, and you may only get one during the first couple of uses. So you can keep taking the medication if you feel the headaches aren’t too bad. A good way to prevent a “Viagra headache” is to drink plenty of water and try to avoid drinking too much alcohol. 

If you get a particularly bad headache and feel as though the medication is causing you discomfort, it’s better to ask your prescriber about changing the dose (or your medication) to see if that helps.

Uncommon Sildenafil side effects

Uncommon side effects may affect up to 1 in 100 people. These include:
  • vomiting
  • skin rash
  • eye irritation
  • bloodshot eyes/red eyes
  • eye pain
  • seeing flashes of light
  • visual brightness
  • light sensitivity
  • watery eyes
  • pounding heartbeat
  • rapid heartbeat
  • high blood pressure
  • low blood pressure
  • muscle pain
  • feeling sleepy
  • reduced sense of touch
  • vertigo
  • ringing in the ears (tinnitus)
  • dry mouth
  • blocked or stuffy sinuses
  • inflammation of the lining of the nose (symptoms include runny nose, sneezing and stuffy nose)
  • upper abdominal pain
  • gastroesophageal reflux disease (symptoms include heartburn)
  • blood in urine
  • pain in the arms or legs
  • nosebleed
  • feeling hot
  • feeling tired

Rare Sildenafil side effects

Rare side effects may affect up to 1 in 1,000 people, and include:
  • fainting
  • stroke
  • heart attack
  • irregular heartbeat
  • temporary decreased blood flow to parts of the brain
  • feeling of tightening of the throat
  • numb mouth
  • bleeding at the back of the eye
  • double vision
  • reduced sharpness of vision
  • abnormal sensation in the eye
  • swelling of the eye or eyelid
  • small particles or spots in your vision
  • seeing halos around lights
  • dilation of the pupil of the eye
  • discoloration of the white of the eye
  • penile bleeding
  • presence of blood in semen
  • dry nose
  • swelling of the inside of the nose
  • feeling irritable
  • sudden decrease or loss of hearing

Can Viagra cause a heart attack?

If you take nitrates or certain medications for heart pain, like glyceryl trinitrate spray (GTN) or isosorbide mononitrate, it’s likely Sildenafil won’t be safe for you. 

This is because nitrates can cause a drop in blood pressure, and when combined with Sildenafil increase the risk of a heart attack.[1]

In any case, if you use Viagra and experience chest pain either during or after having sex, you should seek medical attention as quickly as possible.

Other Viagra side effects that may be serious

Let’s take a look at some other serious side effects:
  • Allergic reactions. These could cause symptoms of wheezing; dizziness; swollen face, eyelids, lips or throat; and breathlessness. Anaphylaxis or severe allergic reactions need immediate medical attention. If you have known allergies then you should inform the prescriber and study the ingredient list.
  • Priapism or a prolonged erection can also be dangerous. If you have a painful erection or one that lasts for longer than four hours then you need to go to the hospital.

Are there any long term side effects of Viagra?

The good news is that in most cases, the side effects that can occur when you take Viagra or Sildenafil will ease off once the medication is out of your system. But some of the more serious (and rare) sildenafil side effects can have longer-term implications. 

Just to give an example: priapism can permanently damage cells in the penis if it isn’t treated by a medical professional swiftly. So if you find yourself with an erection that lasts for longer than four hours, get yourself to a hospital urgently.

Men who have genetic eye conditions like retinitis pigmentosa should also avoid Viagra, as it can permanently worsen their visual problems.

Can my partner get side effects from Viagra?

Viagra carries virtually no risk to those who don’t take it, including your sexual partners. It’s very unlikely your partner will experience side effects if you’re taking the Sildenafil pill.

On the subject of partners and pregnancy, there have been studies looking at the impact of Viagra on male fertility. One study concluded that sildenafil did not impact sperm function or quality.[2]

You can always talk to your doctor or pharmacist if you have concerns about Viagra and fertility.

Should I see a doctor about Sildenafil side effects?

It’s a good idea to let your prescriber know if you experience any side effects when taking a medication. This means that your experience of Viagra symptoms can be recorded and reported to the FDA. 

Your doctor can talk through the symptoms you’re experiencing and check whether you’re comfortable to continue with your prescription or whether any changes should be made.

In some cases, your dosage of Viagra can be lowered to try and reduce side effects. (Sometimes it’s just a case of striking the right balance.)

What Viagra side effects you need to go to a hospital with

If you develop chest pain, heartbeat changes, visual problems or a prolonged erection, go to the hospital right away. Don’t take any more Viagra and avoid doing anything physically exertive (which includes having sex).

Can I lower my risk of side effects on Viagra?

There are also some steps you can take to keep your risk of Viagra side effects as low as possible. Make sure you’re open and honest about your medical history when you talk to a prescriber, especially in relation to health conditions and any medication you take, or have taken. 

We know it’s on the hefty side, but read the patient information leaflet. Familiarizing yourself with the instructions, side effects and what to do if taking Viagra doesn’t go exactly to plan can be helpful.

If you get side effects while taking Viagra or Sildenafil, make sure you let your doctor know. They may prefer to keep a closer eye on your use or lower the dose. Doing this means the overall amount of active ingredient you take is reduced, but so too is the risk of side effects. (Most of the time, it should still work just as well.)


[1] Chamsi-Pasha, H. (2001). Sildenafil (viagra) and the heart. Journal of family & community medicine, [online] 8(2), pp.63–6. Available at:

‌[2] Purvis, K., Muirhead, G.J. and Harness, J.A. (2002). The effects of sildenafil on human sperm function in healthy volunteers. British Journal of Clinical Pharmacology, 53, pp.53S60S.