Sildenafil and Viagra Side Effects: The Ultimate Guide

Medically approved by
Dr Earim Chaudry
Last updated
19th August 2021

In 30 seconds…

When you take Viagra, its active ingredient, Sildenafil Citrate, gets to work. This increases blood flow to your penis by acting on the enzymes responsible for muscle contraction within the blood vessels. Of course, as with any medication, there can be side effects, particularly when taking it with other medications. These are, however, usually mild.

Viagra side effects can include dizziness and headache, indigestion, and hot flushes. Blurred vision and nasal congestion can also occur. Older men can expect the same side effects – however, they are thought to be more likely due to increased chances of other medical conditions.

More long-term and serious side effects of Viagra are very rare, but can potentially include erections that just won’t go away, sensory impairment, and digestive problems. These are more likely to be evoked in patients with pre-existing conditions. If you experience any of these, go and see your doctor.

What Happens When You Take Viagra?

Viagra is the most famous treatment for erectile dysfunction (ED), the reduced ability to achieve and sustain an erection. 

When you take Viagra, the active ingredient, Sildenafil Citrate, begins to work its magic. This drug, like other similar drugs – including Tadalafil (which you may know by its brand-name Cialis) and Vardenafil (or Levitra) – is what is known as a PDE5 inhibitor. It tackles the enzyme phosphodiesterase type 5 (PDE5) which is responsible for muscle contraction in your penis. 

It’s through this process that Viagra enables improved blood-flow to where you need it. It widens your blood vessels by blocking the action of the enzyme PDE5, thereby it relaxes the smooth muscle within the vessels supplying the penis, consequently enabling you to get and maintain better erections. Sildenafil is what makes all this happen – and it usually takes about an hour for it to take effect. 

Viagra works successfully in 80% of men. However, we shouldn’t forget that it is a medication. As a result, it can have side effects. And that’s what we’re discussing in this article. Let’s dive in.

What are the Side Effects of Viagra?

Given that Viagra is a drug and a medical treatment, there can be side effects. However, these side effects are usually rare, mild, and temporary, and the benefits to you will usually outweigh the risks. 

The most common Viagra side effects are flushing, headaches, indigestion, dizziness, and changes to your vision. Usually, they will pass quickly – and you can help them on their way with simple measures. If you have a headache, drink water. If you are feeling dizzy – which is most common if you get up too quickly – stay still until it passes. 

Don’t drive until your side effects pass – and, if they don’t go away, inform a doctor as soon as you can.

There are some horror stories of Viagra side effects, including erections that just won’t disappear — as well as sudden hearing loss or vision loss. These are possible and can be dangerous, but they are very rare. They occur in less than 0.1% of men — and most commonly in heavy smokers or those with heart disease or high blood pressure.

Side Effects of Viagra in Older Men? 

There are no known side effects of Viagra that affect older men specifically. However, it’s an unfortunate fact that older people might be more sensitive – particularly older men with pre-existing medical conditions. Always document any medical conditions or other medicines you’ve taken prior to buying and using Viagra – or any erectile dysfunction medication.

Drug Interactions: Taking Viagra with Other Medications

If you are taking medications known as nitrates, which are usually prescribed for chest pain, or guanylate cyclase stimulators for high blood pressure (pulmonary arterial hypertension), it is highly advisable that you avoid taking Viagra (or generic unbranded Sildenafil).

Given that, before it was an erectile dysfunction treatment, Viagra was actually designed by its manufacturer (Pfizer) as a treatment for high blood pressure, the combination can result in severe drops in blood pressure – which can be dangerous. 

The same applies with amyl nitrate medications. The US Food and Drugs Agency (FDA) recommends that you limit your use of Viagra if you are on Ritonavir too.

Talk to your doctor before taking Viagra if you have previously had a heart attack or other heart problems, a stroke, or if you suffer from unstable angina. If you are on medication known as alpha-blockers, it is best to seek medical advice from a health care professional before taking it too. 

Viagra and Alcohol

While not a medication, we should point out that you ought to take care when drinking alcohol when using Viagra. While we know that a wee tipple can help you get in the mood, you will only increase the likelihood of the side effects associated with the use of Viagra. 

That’s not to say that you can’t drink anything at all. However, the warning about blood pressure applies here too. Alcohol brings it down, and so does Viagra. If you have a low blood pressure all ready, this can cause problems – and may get in the way of enjoying any sexual activity.

It is usually not advised, by the way, to take Viagra if you are using cannabis or other recreational drugs.

How Long do Viagra Side Effects Last?

Viagra side effects do not usually last for very long. The more common side effects, including headaches, dizziness, and a blocked or stuffy nose, should pass quickly – and headaches can be treated by drinking water and taking over-the-counter painkillers such as paracetamol. 

Remember that the effects of Viagra usually last for about four hours. After this, your side effects should have passed. If you still have an erection after this time – and if it is painful – consult a doctor immediately. This prolonged erection might be what is known as priapism and can be damaging for your penis.

Are There Any Long-term Side Effects From Using Viagra?

Whilst most of the Viagra side effects are temporary and mild, long-term side effects are incredibly rare. These include potential problems with the digestive system, with the cardiovascular system, and in your hearing and vision. 

The PDE5 enzymes that it tackles are also to be found in the eyes, meaning that, with prolonged use, your vision can become blurred, discoloured, or suffer temporary impairment. Meanwhile, incontinence and difficulties ejaculating have been reported, but these side effects are uncommon. 

Importantly, people who use the drug over long periods of time – and young men in particular – can experience another long-term side effect of Viagra: psychological dependence. When people who don’t have ED use Viagra or generic unbranded Sildenafil, they can ultimately become reluctant to have sex without it. Only those who need the drug should take it. 

Finally, for those wondering, there is no evidence that the effectiveness of Viagra decreases over time. So, you won’t build up a tolerance to it if you use it a lot. 

What Should You Do If You Don’t Tolerate Viagra?

Unfortunately, it happens: men sometimes don’t get on with Viagra. However, this doesn’t mean that you can’t get treatment for ED. Instead, you can consider two options. 

Take a lower dose. The standard dose for Viagra is 50mg. However, for men who do not tolerate this dosage, there is a 25mg alternative that you can try. This should reduce the chance and severity of side effects – although it may affect the success of the medication too.

Try a different ED medication. If after trying the lower dose, you are still troubled by side effects, a different PDE5 inhibitor might be a better option for you. Studies suggest that these may be better tolerated than Viagra. Try Tadalafil, for example. 

Key Takeaways

Viagra is a clinically approved treatment for ED and it is safe and effective in the vast majority of cases. However, there are side effects of Viagra that you should be aware of before you take it. Always read the accompanying Patient Information Leaflet (PIL) for a more comprehensive overview of the side effects.

In the short term, these can include headaches, dizziness, flush, and a blocked nose. However, the long term side effects of Viagra – including loss of vision, abnormal vision, and priapism – are potentially more serious. If in doubt, give us a call – our medical team will gladly guide you.


  1. VIAGRA (sildenafil citrate) tablets -Full Prescribing Information:

  2. -Viagra Side Effects:

  3. James G McMurray, Robert A Feldman, Stephen M Auerbach, Herb DeRiesthal, Neal Wilson (2007). Long-term safety and effectiveness of sildenafil citrate in men with erectile dysfunction:

While we've ensured that everything you read on the Health Centre is medically reviewed and approved, information presented here is not intended to be a substitute for professional medical advice, diagnosis, or treatment. It should never be relied upon for specific medical advice. If you have any questions or concerns, please talk to your doctor.

Further reading

From our health centre. Experts, information and hot topics. See all Erectile Dysfunction articles

Ed by Manual

Erectile dysfunction treatments

Erections aren’t always easy for millions of men in the UK. It’s no big deal. Choose from highly effective, clinically proven solutions.