As with any medication, there are risks of side effects associated with Viagra and sildenafil that should be understood before you start the treatment. While these are relatively rare and mild when taken as directed (such as a stuffy nose), in rare cases they can be more severe or debilitating (sudden vision loss is an example)

Your prescribing clinician should be able to inform you of the risks involved and their likelihood when prescribing you the treatment. The patient information leaflet that comes with your medication also lists all known side effects as well as their frequency. It should be noted that medication for erectile dysfunction rarely causes noticeable issues once the right dosage has been found and that most men will find that the results of their use outweigh the mild side effects that might occur.

Viagra results from clinical trials

All medications undergo rigorous clinical trials to check whether the medication in question is safe for use. In the case of Viagra, and its generic version sildenafil, there have been several trials over the course of the last 25 years. Some of these suggested that the discontinuation rate for those who took a placebo (a tablet not containing any active ingredient) was higher than in those who took sildenafil, although finding the right dosage was found to be important in minimising the risk of side effects.

Sildenafil side effects and their frequency

According to the patient information leaflet for Viagra, common and very common side effects are mild:

Very common (may affect more than 1 in 10 people): Headache.

Common (may affect up to 1 in 10 people): Nausea, flushing, hot flush, indigestion, changes of colour in vision, blurred vision, visual disturbance, blocked sinuses and dizziness.

Less common side effects occasionally listed more severe side effects.

Uncommon (may affect up to 1 in 100 people): 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, dry mouth, blocked or stuffy sinuses, inflammation of the lining of the nose, upper abdominal pain, gastro-oesophageal reflux disease, presence of blood in urine, arm and leg pain, nosebleed, feeling hot and feeling tired.

Rare (may affect up to 1 in 1,000 people): 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, discolouration of the white of the eye, penile bleeding, presence of blood in semen, dry nose, swelling of the inside of the nose, feeling irritable and sudden decrease or loss of hearing.

Some visual problems have also been reported for Viagra, eye floaters being one of the more common. Some studies have suggested that there is a small increase in the risk of developing gout when taking Viagra.

Viagra with food and drink

Viagra’s effects, like all oral PDE-5 inhibitor erectile dysfunction treatments, can be greatly slowed when taken after a large meal, particularly one containing a lot of fat. When taken with large amounts of alcohol, there might be a risk of your blood pressure becoming low, although the larger risk is that alcohol is a major cause of erectile dysfunction and may prevent Viagra and sildenafil from working properly.

Side effects of Viagra and sildenafil with other medications

Like all newer types of erectile dysfunction treatments, including Cialis, Viagra and sildenafil might interact with other medications. In particular, you should avoid use of nitrates (such as the recreational drug amyl nitrate). This is due to the fact that low pressure side effects can be greatly increased.

Riociguat (which is used in the treatment of high blood pressure in the lungs) may also cause greater hypotensive (low blood pressure) side effects.

Reporting Viagra side effects

If you experience any side effects with these medications, you can report them using the government’s yellow card scheme. This helps the MHRA track and update its data for all treatments in order to provide patients and doctors with the most complete data possible.

Page last reviewed:  23/07/2020