Doses range from 25 milligrams to 100 milligrams, depending on the drug's effect. The usual dose is 50 milligrams. If you are over 65, have liver or kidney problems, or are taking erythromycin, ketoconazole, itraconazole, ritonavir, or saquinavir a dose of 25 milligrams may be sufficient. Your doctor will adjust the dosage if the drug is not working properly for you.
Take Viagra only before sexual activity. The manufacturer recommends a maximum of 1 dose per day (1 dose every 2 days for those taking ritonavir).
To avoid low blood pressure, do not take the 50-milligram or 100-milligram dose of Viagra within 4 hours of taking an alpha-blocking drug such as Cardura.