Viagra Side Effects: How Common They Are and When to Get Help

Side effects are common with Viagra (sildenafil), but they are usually mild. Headache is the most common, affecting more than 1 in 10 men. Flushing, a blocked nose, indigestion and dizziness follow. These usually fade within a few hours as the tablet wears off. Serious problems are rare, but a few need action straight away, so read the next section first.

Get help straight away if#

• Your erection lasts more than 4 hours (priapism). Go to A&E. Waiting can cause permanent damage.
• You suddenly lose vision in one or both eyes. Stop taking sildenafil and go to A&E or call 999.
• Your hearing suddenly drops, with or without ringing or dizziness. Stop taking it and get urgent help from A&E or NHS 111.
• You get chest pain during sex. Stop. Call 999 if it does not ease quickly. Do not use your own GTN spray within 24 hours of sildenafil. Tell the call handler and paramedics you took it.
• Your lips, face or tongue swell, you wheeze, or you get a spreading rash. Call 999. This could be an allergic reaction.

How common each side effect is#

The UK patient leaflet groups side effects by how many men get them. Here is how that looks for Viagra.

Side effects are dose-related. They are more likely at 100mg than at 50mg or 25mg. Viagra Connect is 50mg only, with a limit of one tablet in 24 hours. Prescription Viagra comes in 25mg, 50mg and 100mg, and you take it once a day at most.

Men over 65, or with liver or kidney problems, are often started on 25mg. For more on heart risk, see our guide on whether Viagra can cause a heart attack.

Why one tablet affects more than the penis#

Sildenafil blocks an enzyme called PDE5. PDE5 breaks down a chemical messenger called cGMP. When cGMP builds up, the muscle in blood vessel walls relaxes and more blood flows in. With sexual arousal, that produces an erection.

PDE5 also sits in other parts of the body. Relaxed vessels in the head, face and nose explain headache, flushing and a blocked nose. A small drop in blood pressure explains dizziness. Effects on the gut muscle cause indigestion. Sildenafil also weakly blocks a related enzyme in the eye, which can tint your vision blue or make it blurry.

The tablet works in 30 to 60 minutes and lasts up to about 4 hours. Most side effects follow the same timing. Our guide on how long Viagra lasts covers this in more detail.

Easing the common ones#

• Headache: Paracetamol and a glass of water usually help.
• Flushing and a blocked nose: These pass on their own, usually within a few hours.
• Indigestion: An antacid from the pharmacy can help.
• Dizziness: Sit or lie down until it passes. Alcohol also lowers blood pressure, so it makes dizziness worse.

Driving and machinery: Dizziness and visual changes are common with sildenafil. Check how the tablet affects you before you drive or operate machinery. Do not drive or use machinery if you feel dizzy or your vision is affected.

If side effects keep coming back, tell a pharmacist or prescriber. A lower dose may suit you better. Do not take a second tablet to make up for a weak effect. Tadalafil and vardenafil are other options. Each has its own pattern of side effects. Tadalafil, for example, often causes back and muscle aches.

Check these before you take it#

Do not take sildenafil if you:

• Use any nitrate, such as GTN spray or tablets, isosorbide mononitrate or isosorbide dinitrate. Nicorandil and poppers (amyl nitrite) count too. Together they can drop your blood pressure dangerously. Do not use a nitrate within 24 hours of a sildenafil tablet.
• Take riociguat, a medicine for pulmonary hypertension.
• Are allergic to sildenafil or any ingredient in the tablet.
• Have ever lost vision in one eye from a condition called NAION (an optic nerve problem). Sildenafil must not be taken again.
• Have an inherited eye condition such as retinitis pigmentosa.
• Have had a heart attack or stroke recently, or have unstable angina or severe heart failure.
• Have very low blood pressure or severe liver problems.
• Have been told sex is too strenuous for your heart.

Ask a pharmacist first if you take:

• An alpha-blocker, such as tamsulosin or doxazosin. Together they can cause dizziness or fainting.
• Other blood pressure tablets.
• Ritonavir or another HIV protease inhibitor. The limit is 25mg in 48 hours, and a prescriber must decide.
• Erythromycin or ketoconazole. They raise sildenafil levels, so a lower dose may be needed.

Also tell them if you have sickle cell disease, leukaemia, myeloma or a curved penis (Peyronie's disease). These raise the risk of priapism. Diabetes, high blood pressure, high cholesterol, smoking and a small, crowded optic disc raise the risk of NAION.

For Viagra Connect, a pharmacist asks these questions before they sell it to you. It is for men aged 18 or over. The MHRA reclassified it as a pharmacy medicine in 2017. The pharmacist will refer you to a GP if you have heart disease, take nitrates, or your ED is new and unexplained.

Taking it for years, and when to get checked#

Sildenafil has been used for ED since 1998. The leaflet lists no side effect that builds up with repeated use. The risk comes with each dose, so the checks above matter every time.

Speak to a pharmacist or GP if side effects bother you or keep returning. Do the same if you start a new medicine. ED can also be an early sign of heart disease, diabetes or low testosterone, so a GP check of your blood pressure, blood sugar and cholesterol is worthwhile.

Buy only from a GPhC-registered pharmacy. You can check the register at pharmacyregulation.org. Pills from unregulated sites can be fake, with the wrong dose or other drugs in them.

If you would like a UK prescriber to check that sildenafil suits you, you can start a free consultation with Totiva. You only pay once treatment is approved.