How well does Viagra work?

For most men with erectile dysfunction it works — but not for every man, and never without arousal. In the fixed-dose studies behind its European licence, the share of men who reported better erections was 62% on 25 mg, 74% on 50 mg and 82% on 100 mg, against 25% on placebo, and the effect held up in long-term studies (EMA product information). Viagra is a brand of sildenafil, so the figures describe sildenafil.

How well it works depends on the cause. Across all the studies, improvement was reported by 84% of men whose erectile dysfunction was psychological, 68% where the cause was physical, 59% of men with diabetes and 43% after removal of the prostate (radical prostatectomy). Why it fails some men, and what can be done then, is covered in does Viagra work for every man with erectile dysfunction?

On its own, sildenafil does not cause an erection. It blocks an enzyme called PDE5, which lets more blood flow into the penis when you are sexually aroused (EMA) — the mechanism in full is in how Viagra works and whether it is effective. That also answers does Viagra make you harder?: in men with erectile dysfunction it makes an erection easier to get and keep, which is what the studies measured. Its site of action is the penis, not desire. The hour after the first tablet — the wait, the need for arousal, side effects such as flushing or a blocked nose — is described in what does it feel like to take Viagra?

Does Viagra make you last longer in bed?

Not directly. Viagra's medicine, sildenafil, is licensed to treat erectile dysfunction — trouble getting or keeping an erection — not premature ejaculation, so on its own it does not delay coming (EMA). The full answer, including what it can change for men whose early ejaculation goes with erection problems, is in does Viagra make you last longer in bed?

Three narrower questions have their own pages. Does sildenafil increase the duration of sexual activity? looks at what studies measured in men with and without erectile dysfunction; can Viagra shorten the refractory period? at the wait before you can go again. None of the labels says Viagra keeps an erection going after you come — see can Viagra keep you hard after ejaculation? If coming too soon is the real problem, its treatments are compared in our guide to lasting longer in bed.

How long does Viagra take to work?

Usually 30 to 60 minutes (healthdirect), which is why the label says to take it about an hour before sex (EMA). In a laboratory study of men who had not eaten, the median time to an erection firm enough for sex was 25 minutes, with a range of 12 to 37 minutes. Food slows it down: taken with a meal, sildenafil is absorbed more slowly and reaches its peak in the blood about an hour later on average (EMA product information). More on the timing in how long does sildenafil take to work?

Letting a tablet dissolve under the tongue is a different route; what is known about it is in the duration and effectiveness of sublingual sildenafil. The Australian leaflet says to swallow the tablet whole with a full glass of water (Viagra CMI). Which of the ED medicines starts soonest is compared in the fastest-acting ED medications.

How long does Viagra last?

Up to about 4 hours. "The effects of the medicine can last for up to 4 hours" (healthdirect), and in a laboratory study sildenafil could still produce an erection in response to sexual stimulation 4 to 5 hours after the dose (EMA product information). That is a window in which arousal can lead to an erection, not an erection that lasts 4 hours. An erection that lasts more than 4 hours needs urgent care at the nearest hospital emergency department (healthdirect). The detail is in how long does sildenafil last?

The medicine itself clears steadily: sildenafil's half-life is 3 to 5 hours (EMA product information) — see how long Viagra stays in the body. How timing, effect and side effects fit together is summarised in Viagra's duration, effectiveness and side effects. A longer window belongs to a different medicine: tadalafil, the medicine in Cialis, "has been proven to be effective for up to 36 hours" (Cialis CMI).

Is 20 mg of sildenafil enough for erectile dysfunction?

20 mg is not one of the erectile dysfunction doses on the label. For ED, sildenafil starts at 50 mg and can be lowered to 25 mg or raised to 100 mg (EMA). 20 mg is the tablet strength of Revatio, the sildenafil brand for pulmonary arterial hypertension, taken three times a day (EMA). What 20 mg can and cannot do for erections is in is 20 mg of sildenafil effective for ED? For comparison, the lowest ED dose, 25 mg, helped 62% of men in the fixed-dose studies. Your GP chooses the dose; the label doses are set out on our Viagra dosage page.

How can you make Viagra work better?

Use it the way the label describes. Take it about an hour before sex, and not straight after a big meal: "You may find VIAGRA takes longer to work if you take it with a heavy meal". Allow for arousal — "VIAGRA will work only if you are sexually excited" — and go easy on alcohol, because "Drinking alcohol can temporarily impair the ability to get an erection" (Viagra CMI). If it still does not help, tell your doctor, who can change the dose or the treatment (healthdirect). The practical list is in how to increase the effects of Viagra.

Does Viagra affect sperm or fertility?

Not on the evidence in its label. "There was no effect on sperm motility or morphology after single 100 mg oral doses of sildenafil in healthy volunteers" (EMA product information). The label makes no claim about repeated use or about the chance of conception; the research on both is reviewed in does sildenafil affect sperm quality and fertility? and can Viagra affect male fertility or the chances of conception?

Viagra, Cialis or Levitra: which works best?

The labels do not rank them: they work the same way and differ mainly in timing. The PDE5 inhibitors available in Australia are sildenafil (Viagra), tadalafil (Cialis), vardenafil and avanafil (Spedra) (healthdirect); tadalafil can work for up to 36 hours, sildenafil for up to 4. The Levitra brand is not on the Australian Register of Therapeutic Goods, though generic vardenafil is. The three brands are set side by side in Viagra vs Cialis vs Levitra, and the head-to-head questions — Kamagra vs Viagra, sildenafil vs tadalafil — on our ED medicine comparisons page. For the choice itself, see which erectile dysfunction drug is best.

Settled on sildenafil?

Every figure on this page is for sildenafil, the medicine in Viagra. Kamagra is sildenafil too, 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. If you take any heart or blood-pressure medicine, talk to your GP before your first dose.

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