How well does Viagra work in clinical trials?

In fixed-dose trials most men reported better erections: "62% (25 mg), 74% (50 mg) and 82% (100 mg) compared to 25% on placebo." Sildenafil, the medicine in Viagra, was given to "more than 8 000 patients aged 19-87" in clinical studies; "the discontinuation rate due to sildenafil was low and similar to placebo", and "The safety and efficacy of sildenafil was maintained in long-term studies" (EMA product information). It works only with sexual stimulation, and its common side effects are headache, facial flushing, a blocked nose and indigestion (healthdirect). What users and studies report is gathered in reviews and effectiveness of Viagra; how quickly it works and how long it lasts are in our guide to how well Viagra works.

Does a higher dose of sildenafil work better?

In the trials the response rose with the dose, and the label lets your doctor adjust it within 25 to 100 mg. The recommended dose is 50 mg about an hour before sex; it may be increased to a maximum of 100 mg or decreased to 25 mg depending on how well it works and the side effects, and it is taken at most once a day (EMA). "You should not take any more than one sildenafil tablet in 24 hours" (healthdirect). The dose-by-dose picture is in how well sildenafil citrate works at different doses, and whether 100 mg is too much in our dosage guide.

Does it work as well with diabetes or after prostate surgery?

It works for fewer men in some groups: across all studies, improvement was reported by 59% of men with diabetes and 43% after radical prostatectomy. The label's other figures: psychogenic erectile dysfunction 84%, organic 68%, older men 67%, high blood pressure 68%, ischaemic heart disease 69%, spinal cord injury 83% (EMA product information). Heart disease and blood pressure also decide whether you can take it at all — see our guide to ED medicines with diabetes and other conditions; after surgery, see ED after an operation.

What if Viagra doesn't work for you?

Talk to your doctor: healthdirect says "If you are not finding sildenafil effective in treating your erectile dysfunction, speak to your doctor about changing the dose or treatment option." Two things can make it look as if it failed: it needs sexual stimulation, and "You may find VIAGRA takes longer to work if you take it with a heavy meal" (Viagra CMI). The rest is in our guides to making Viagra work better and the other treatments for erectile dysfunction.

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