What are Viagra's side effects, and how common are they?
Headache affects 1 man in 10 or more; dizziness, flushing, a blocked nose, nausea, indigestion and a change in vision affect up to 1 in 10. The frequencies come from 74 placebo-controlled studies in 9,570 men, plus reports since launch, and in the controlled studies the rate of stopping because of sildenafil "was low and similar to placebo" (sildenafil label). The common ones "usually go away after a few hours" (healthdirect).
| How often, on the label | Side effects of sildenafil (Viagra) |
|---|---|
| 1 in 10 or more | Headache |
| 1 in 100 to 1 in 10 | Dizziness; flushing and hot flushes; a blocked nose; nausea and indigestion; colour-tinged, blurred or disturbed vision |
| 1 in 1,000 to 1 in 100 | A fast heartbeat and palpitations; high or low blood pressure; nosebleeds; reflux and vomiting; rash; muscle pain; chest pain; blood in the urine; ringing in the ears; eye pain and sensitivity to light |
| Rarer than 1 in 1,000 | Fainting; heart attack and irregular heart rhythm; stroke; sudden deafness; and — reported only since it came onto the market — seizures, sudden loss of sight (NAION) and priapism |
Source: EMA — Viagra product information, section 4.8.
The same list in the words of the Australian leaflet, with what to do about each: what are the side effects and health risks of taking Viagra? Symptom by symptom — headache, flushing, eyesight, hearing, overdose — and how Cialis and vardenafil compare, is on our side effects of ED medicines page.
Does Viagra affect your heart rate and blood pressure?
It lowers blood pressure a little, for a short time; a faster heartbeat is an uncommon side effect. "Sildenafil causes mild and transient decreases in blood pressure which, in the majority of cases, do not translate into clinical effects": after 100 mg, lying-down blood pressure fell on average by 8.4 mmHg (systolic) and 5.5 mmHg (diastolic) at its lowest, and single doses of up to 100 mg in healthy volunteers had no clinically relevant effect on the heart's electrical trace (ECG). A fast heartbeat, palpitations and an increased heart rate are uncommon side effects on the same label. The two questions in full: does sildenafil affect blood pressure and heart rate? and can Viagra or sildenafil change your heart rate?
The small drop matters when something else lowers blood pressure too. With nitrates it becomes "a sudden drop in your blood pressure that is hard to treat" (healthdirect); with alpha-blockers, used for high blood pressure or prostate problems, it may cause symptoms of low blood pressure in a few susceptible men, mostly within 4 hours of the dose (sildenafil label). The full list of medicines is on Viagra and Cialis with other medicines; for men who already have high blood pressure, see what Viagra does to blood pressure in men with hypertension.
Is Viagra safe for your heart?
The risk the leaflet stresses is sex itself. "Because sexual activity may place a strain on your heart, your doctor will need to check whether you are fit enough to take Viagra" (Viagra consumer medicine information). In the label's studies of men with heart disease, a single 100 mg dose did not change how much blood the heart pumped or reduce blood flow through narrowed coronary arteries (14 men with severe coronary artery disease), and in 144 men with stable angina it made no clinically relevant difference to how long they could exercise before angina set in. Heart attacks, sudden cardiac death and irregular rhythms have been reported since it came onto the market, mostly in men who already had cardiovascular risk factors and often during or shortly after sex (sildenafil label). Heart conditions one by one are on our health conditions and ED medicines page; see also does Viagra affect the heart, and is it safe for heart patients?
How likely is priapism on Viagra, and what should you do?
It is rare, and an emergency when it happens: an erection lasting more than 4 hours needs the nearest hospital emergency department (healthdirect). "Very occasionally, sildenafil causes a painful erection or an erection that won't go away (priapism)", says healthdirect; the label lists it among the rare reactions reported only since the medicine came onto the market, where frequencies "cannot be reliably determined". Left untreated, "penile tissue damage and permanent loss of potency could result" (sildenafil label). The Australian leaflet does not wait the full 4 hours when it hurts: "If your erection continues for four hours, or sooner if there is pain, you should seek medical attention urgently" (Viagra consumer medicine information).
Men with sickle cell anaemia, leukaemia or multiple myeloma, or with a curved or scarred penis (Peyronie's disease), are more prone to it, and the label asks for caution in them (sildenafil label). The numbers behind "rare": what is the likelihood of priapism with Viagra and Cialis?
Who should not take Viagra?
Anyone who uses nitrates or amyl nitrite ("poppers"), and men whose heart or blood vessels make sex inadvisable. The Australian leaflet also rules it out after a heart attack or stroke in the last 6 months, with severe liver problems, with blood pressure that "is unusually high or low or is not effectively treated", after loss of vision from NAION, with retinitis pigmentosa, and alongside riociguat (Viagra consumer medicine information). It is "not for use in women", and the label does not cover anyone under 18 — what happens if a young person takes it is in what happens if a child or teenager takes Viagra? The list explained: who should not take Viagra?; condition by condition — heart, stroke, diabetes, kidneys — in which health conditions rule out ED medicines.
Is 100 mg of Viagra riskier than 50 mg?
Side effects rise with the dose, and 100 mg is the ceiling. The label starts at 50 mg and moves up to 100 mg or down to 25 mg "Based on efficacy and tolerability"; 200 mg brought more headache, flushing, dizziness and vision changes without working better. Healthy men over 65 cleared sildenafil more slowly, with about 90% higher blood levels than younger men, though the label sets no lower dose for age (sildenafil label). What changes at the top strength: what is the strength and safety of 100 mg sildenafil?; the dose in full on how much Viagra to take.
The same risks apply to every sildenafil tablet
The side effects on this page belong to sildenafil, the medicine in Viagra, so they apply to Kamagra too — the same nitrate rule, the same 4-hour rule. Kamagra is sold here as tablets and oral jelly with live prices on its page; it is not on the ARTG, and that page explains what this means before you order. Generic sildenafil and tadalafil are on our product list.
Sources
- EMA — Viagra (sildenafil) product information, sections 4.2, 4.3, 4.4, 4.8, 4.9, 5.1 and 5.2
- Viagra consumer medicine information (Australia, October 2024)
- healthdirect — Sildenafil (Viagra) (last reviewed February 2025)
- TGA — NSW individual fined for alleged offences relating to unapproved erectile dysfunction medicines (20 February 2024)
