Viagra (sildenafil) has already helped millions of men all over the world to get back their normal sex life. Take this medicine exactly as prescribed by your health care provider. Usually the patients taking this medicine are supposed to take it about 30-60 minutes before having sex to obtain the best effects. Since you are unlikely to be on any kind of dosing schedule when taking Viagra, if you happen to miss a dose just take it as soon as you remember. Taking two doses at once will not make your treatment more efficient, and your erection firmer than you achieved with just one dosage. In some very rare cases Viagra has been reported to cause certain serious side effects. To avoid these side effects you should tell your health care provider about any abnormal reactions you had in the past (prolonged erection), your habits (smoking), or if you had an episode of severe dehydration not so long ago. Your doctor needs to know your full medical history before prescribing this medicine. Report any of the following conditions to your health care provider in case of having them at the moment or in the past: bleeding disorder, chest pain, blood cell problems, high cholesterol, kidney disease, blood circulation problems, eye disease such as retinitis pigmentosa, stomach ulcer, stroke, liver disease, high or low blood pressure, conditions affecting the shape of the penis, heart attack, heart disease, irregular heartbeat, and any other ones you have but that did not appear on this list.