Viagra (Sildenafil) Side Effects, and Who Should Not Take It

Short answer: Sildenafil, the medicine in Viagra, is licensed in the UK for erection problems, and like all medicines it can cause side effects. Very common / common side effects include headache, dizziness, flushing, nasal congestion, dyspepsia (indigestion), nausea and vision disturbances. In the UK product information (Viagra SmPC, section 4.8), headache is the one very common side effect, affecting more than 1 in 10 men, and the others are common, affecting up to 1 in 10. Never take it with nitrates in any form, including poppers, or with riociguat or vericiguat. Get help straight away for chest pain during or after sex, an erection lasting longer than 4 hours, or a sudden loss of sight or hearing (see the safety box below). A GPhC-registered pharmacist reviews every consultation before anything is supplied. Less common side effects are listed in the leaflet in your pack. Please read it before your first dose.

This guide sets out what the UK product information for Viagra and generic sildenafil and the NHS say, as of October 2026: how often each side effect happens, why the common ones happen, which need urgent help, blood pressure, the heart, blood thinners, older men, and who should not take it. Viagra Connect, which is supplied after a pharmacist consultation, with no prescription needed, contains the same medicine, sildenafil, at 50mg.

What are the side effects of Viagra?

Headache is the most common side effect of Viagra (sildenafil), affecting more than 1 in 10 men. Dizziness, flushing, a blocked nose, indigestion, feeling sick and changes to vision, such as a colour tinge or blurred vision, are common, affecting up to 1 in 10. The table gives every side effect in section 4.8 of the UK product information, in plain words, by how often it was reported.

* Reported only since the medicine came into use, not in the trials. The product information says how often these reports happen cannot be reliably worked out, and lists them in its rare column.

Source: Viagra 50 mg film-coated tablets, Summary of Product Characteristics, section 4.8 (emc 7980, text revised December 2025). It lists the side effects reported more often than with a dummy tablet (placebo) across 74 trials in 9,570 men, and medically important reports since. The product information for a generic sildenafil (Amarox, emc 13550, revised August 2026) gives the same list. Less common side effects are listed in the leaflet in your pack. Please read it before your first dose.

Each medicine's list comes from its own product information, so lists for different medicines cannot be compared to show that one causes fewer side effects. For tadalafil (Cialis), see our tadalafil page; forhow the erectile dysfunction tablets differ, see sildenafil vs tadalafil.

Why does Viagra give you a headache, flushing or a blocked nose?

Sildenafil widens blood vessels, and headache, flushing and a blocked nose are among its most common effects, although the product information does not give a separate cause for each. It describes sildenafil as having vasodilator properties, meaning it relaxes and widens blood vessels (SmPC 4.4), and puts the small fall in blood pressure it causes down to this (SmPC 5.1). It links the colour tinge some men notice to a related enzyme in the eye, PDE6 (SmPC 5.1).

The same action is how it helps an erection: when you are aroused, a chemical signal relaxes the blood vessels in the penis so blood can flow in, and sildenafil slows the breakdown of that signal (SmPC 5.1). These tablets only work with sexual stimulation.

How can you reduce the side effects of sildenafil?

• Tell us if a side effect bothers you or does not go away. The NHS says a pharmacist or doctor may be able to advise you how to reduce it.
• Sildenafil: avoid grapefruit and grapefruit juice. The NHS says grapefruit can make side effects more likely.
• Never take more than one tablet in 24 hours. The product information's limit is once a day (SmPC 4.2).
• Keep alcohol light. The NHS advises against drinking too much with sildenafil, because it can make getting an erection more difficult. Drinking less alcohol can help your erections.
• If you feel dizzy or your vision is blurred, do not drive, ride a bike or use machinery until it passes, the NHS advises. These tablets can affect your ability to drive or use machines.

When you reorder, we ask how your last tablets worked and whether you had any side effects. You can choose the same dose or, where there is one, a lower strength, and the pharmacist checks your answers before anything is sent.

Which side effects need urgent help?

Get help straight away for chest pain, dizziness or fainting during or after sex, an erection lasting longer than 4 hours, or a sudden change in or loss of your sight or hearing. These are the warnings every Solira erectile dysfunction consultation gives:

• Cardiovascular symptoms. Stop and call 999 if you get chest pain, dizziness or fainting during or after sexual activity. Do not take another dose.
• Prolonged erection. Seek emergency treatment for an erection lasting longer than 4 hours. This is a medical emergency.
• Vision changes. Stop treatment and contact a doctor if you notice any sudden change or loss of vision.
• Sudden hearing loss. Stop the medication and seek urgent medical attention if your hearing suddenly drops or is lost in either ear.

Why they matter, from the UK product information: if a prolonged erection (priapism) is not treated straight away, the tissue of the penis can be damaged and the ability to have erections lost for good (SmPC 4.4). A sudden loss of vision can be NAION, a rare condition in which the blood supply to the optic nerve is suddenly reduced, reported with sildenafil and similar medicines (SmPC 4.4); anyone who has lost the sight of one eye from NAION must not take sildenafil (SmPC 4.3). A sudden loss of hearing is listed as rare (SmPC 4.8).

The NHS also lists as serious: an allergic reaction (a swollen throat or tongue, a raised itchy rash, difficulty breathing); blistering skin around the mouth, eyes, nose or genitals with flu-like symptoms; signs of a heart attack, such as chest pain that feels tight or squeezing, shortness of breath and sweating; a fast or irregular heartbeat; fits (seizures); and fainting. It says to call 999 for a suspected severe allergic reaction (anaphylaxis), heart attack or seizure, and NHS 111 for any other serious side effect.

Is Viagra safe?

For most men, yes: sildenafil is licensed in the UK to treat erectile dysfunction in adult men, the NHS says most adults can take it, and in its trials few men stopped because of side effects (the product information calls the rate low and similar to placebo, SmPC 5.1). It is not safe for everyone. Not suitable if you take:

• Nitrates in any form, including nicorandil or amyl nitrite (poppers)
• Riociguat (Adempas) or vericiguat (Verquvo)
• An HIV protease inhibitor (atazanavir, darunavir, ritonavir, fosamprenavir, lopinavir, saquinavir or tipranavir)
• Ketoconazole, itraconazole, voriconazole or clarithromycin
• Or have severe cardiovascular disease

Our consultation also does not supply sildenafil if any of these apply, among other reasons:

• Nitrates in any form, including nicorandil or amyl nitrite (poppers)
• Stroke or heart attack in the last 6 months
• Unstable angina, or angina during intercourse
• A heart condition for which a doctor has told you to avoid sex or strenuous activity
• Heart valve disease that is more than mild (for example aortic stenosis)
• Heart failure that limits your everyday activity in the last 6 months
• Uncontrolled heart rhythm problem (arrhythmia)
• Severe liver impairment
• A bleeding disorder
• An active stomach ulcer
• Loss of sight in one eye from NAION (a sudden loss of blood supply to the optic nerve), whether or not it happened while taking an erectile dysfunction medicine
• Retinitis pigmentosa or another inherited condition of the retina
• Very low blood pressure, below 90/50

The consultation asks about your heart, blood pressure, eyes, liver and kidneys and every other medicine you take, and a GPhC-registered pharmacist reviews your answers before anything is sent. If they cannot approve your order, we refund you in full.

Sildenafil from an unregulated website may not be genuine: the NHS warns that many websites sell fake medicines, which can cause unpleasant side effects, and advises checking that an online pharmacy is registered with the General Pharmaceutical Council. QuickCare Pharmacy, the registered pharmacy that dispenses Solira orders (GPhC 9013213), is on that register. See how to check your medicine is genuine. Do not use unlicensed herbal remedies for erections, and do not stop any prescribed medicine unless your doctor tells you to.

Is Viagra bad for your heart?

Not for most men, but sex itself puts some strain on the heart, and sildenafil is not suitable for men with severe heart disease. The UK product information says there is a degree of risk to the heart with sexual activity, so heart health should be considered before any treatment for erectile dysfunction (SmPC 4.4).

Since it came into use, serious heart and circulation problems have been reported in men taking Viagra, including heart attack, unstable angina, sudden cardiac death, abnormal heart rhythms, stroke and mini-stroke, and high and low blood pressure. The product information says most, but not all, of these men had existing risk factors for heart disease, many of the events happened during or shortly after sex, and it is not possible to determine what the events were directly related to (SmPC 4.4). In its table, heart attack and unstable angina are rare, up to 1 in 1,000 men (SmPC 4.8). In a trial of 144 men with stable angina, taking their usual angina medicines other than nitrates, sildenafil made no clinically relevant difference to how long they could exercise before angina stopped them (SmPC 5.1).

Our sildenafil page answers the question of heart disease like this: This depends on the nature and severity of your condition. Sildenafil may be suitable if your blood pressure is controlled, you have mild heart valve disease or mild heart failure that does not limit your everyday activity, or you have had a successful bypass, stent or angioplasty. It is not suitable within 6 months of a heart attack or stroke, with unstable angina or angina during sex, or if a doctor has told you sex is not safe for you. Men who take nitrates cannot take it. Your prescriber will assess your cardiovascular history carefully.

In the consultation we ask which risk factors for heart disease apply to you, including:

• Uncontrolled high blood pressure
• High cholesterol
• Diabetes
• Smoking
• Obesity
• Physical inactivity
• Family history of cardiovascular disease

If three or more apply, we cannot supply treatment until your GP has assessed your heart health. Once your GP is happy, treatment may still be an option. Chest pain, breathlessness, palpitations or faintness with everyday activity need to be checked by a doctor before erectile dysfunction treatment can be considered.

• If you have chest pain now, or feel very unwell, call 999
• If you need advice today, call NHS 111
• Otherwise, please make an appointment with your GP

Can you take Viagra with high blood pressure, and does it lower blood pressure?

Often yes, if your blood pressure is treated and stable, and sildenafil does lower blood pressure a little. After a single 100mg dose, the average largest fall, measured lying down, was 8.4 mmHg in the top (systolic) number and 5.5 mmHg in the bottom (diastolic) number. The UK product information calls these falls mild and transient, and says that in most cases they have no clinical effect (SmPC 5.1).

• With blood pressure medicines: when the trials pooled men taking the main types, including diuretics, beta-blockers, ACE inhibitors, calcium channel blockers and alpha-blockers, side effects on sildenafil were no different from placebo. In men with high blood pressure taking amlodipine, a 100mg dose lowered blood pressure, measured lying down, by a further 8 mmHg (systolic) and 7 mmHg (diastolic), about the same as sildenafil alone. The product information advises caution starting sildenafil with sacubitril/valsartan (SmPC 4.5).
• With an alpha-blocker (such as tamsulosin or doxazosin, often used for prostate symptoms or blood pressure): a few men get low blood pressure with symptoms such as dizziness, most likely within 4 hours of the tablet. The product information says the alpha-blocker dose should be stable first and a 25mg start considered (SmPC 4.2, 4.4 and 4.5).

What our consultation does:

• Very low blood pressure, below 90/50: we do not supply sildenafil, and its product information rules it out too (SmPC 4.3).
• We ask for your blood pressure reading. A reading from the last 12 months, from a home monitor, a pharmacy or your GP. If you have not had it checked in the last 12 months, we flag that for the pharmacist and ask you: Please have your blood pressure checked soon, at a pharmacy or by your GP. A reading above 170/100 is flagged for the pharmacist too.
• Uncontrolled high blood pressure counts as one of the risk factors for heart disease above.
• Blood pressure medicines: taking them is a caution the pharmacist reviews before supply, not a reason on its own to stop.
• With an alpha-blocker, its dose must have stayed the same recently without dizziness or fainting, and you start on 25mg, the lowest strength.

Can you take Viagra with blood thinners?

A blood thinner does not on its own rule out sildenafil, but the pharmacist needs to know about it. The UK product information found no significant interaction with warfarin, and sildenafil did not add to the effect of aspirin on bleeding time (SmPC 4.5). It gives no results for other blood thinners. It has no safety information for men with a bleeding disorder or an active stomach ulcer, and says sildenafil should be given to them only after careful weighing of benefit and risk (SmPC 4.4); we do not supply it to anyone with either. Nosebleeds are an uncommon side effect, up to 1 in 100 men (SmPC 4.8). List every medicine you take in the consultation, including any blood thinner.

Are the side effects different in older men?

The UK product information does not list different side effects for older men, and says no dose change is needed at 65 or over (SmPC 4.2). Healthy men aged 65 or over did clear sildenafil more slowly, so it reached higher levels in their blood than in younger men (SmPC 5.2).

So a lower start is not automatic with age. In our consultation, sildenafil starts at 50mg, or at 25mg if you take an alpha-blocker, have a liver problem, or take erythromycin, aprepitant, diltiazem, fluconazole or verapamil, and the pharmacist decides. The checks on your heart, blood pressure and other medicines apply at every age. Our consultation for prescription sildenafil has no upper age limit; we supply Viagra Connect to men aged 18 to 64.

Does Viagra have long-term side effects?

The UK product information does not list any side effect that comes from taking sildenafil over a long time, and says its safety was maintained in long-term studies (SmPC 5.1). The longer-term point is the cause of the erection problems: the NHS says erection problems that keep happening might be a sign of a health condition that can be treated, such as high blood pressure, high cholesterol or diabetes. If this is your first time with erection problems, see your GP to check your blood sugar, cholesterol and testosterone, and have a heart health check at least every 5 years.

Erection problems can also be a side effect of other medicines, the NHS notes, so tell us every medicine you take. A single 100mg dose had no effect on how sperm move or look in healthy men (SmPC 4.6). If you keep using sildenafil, a review is needed every 6 to 12 months, and each repeat order asks about your health again.

Does a higher dose mean more side effects?

It can: the UK product information says that in studies, doses twice the 100mg maximum did not work better but did cause more side effects, such as headache, flushing, dizziness, indigestion, a blocked nose and changes to vision (SmPC 4.9). Its table does not give separate rates for each strength (SmPC 4.8).

That is why the usual dose is 50mg about an hour before sex, raised to 100mg or lowered to 25mg depending on how well it works and how well you tolerate it, never above 100mg and never more than once a day (SmPC 4.2). We supply 25mg, 50mg, 100mg tablets. Never take more than one tablet in 24 hours. The pharmacist decides your dose: more on our sildenafil page. A heavy or high-fat meal can delay how quickly it works. For timing and how long it lasts, see how long sildenafil lasts.

Are Viagra Connect's side effects the same?

Viagra Connect contains the same active ingredient, sildenafil, at 50mg, and has its own leaflet with its own list of side effects. Common side effects include headache, flushing, indigestion, a stuffy nose, dizziness, feeling sick and changes to your vision, such as a colour tinge or blurred vision. These are usually mild to moderate and short-lived. Less common side effects are listed in the leaflet in your pack. Please read it before your first dose.

We supply Viagra Connect after a pharmacist consultation, to men aged 18 to 64. Erection problems can be an early sign of heart disease, diabetes or high blood pressure. If you use Viagra Connect, book a check-up with your GP as soon as you can, within 6 months of starting it. For what else differs, see Viagra Connect vs prescription sildenafil, or all our erectile dysfunction treatments.