Viagra (sildenafil citrate) is a PDE5 drug that can be prescribed for the treatment of male impotence. This condition affects men that are still quite young and may involve partial or complete inability to get an erection and have sex. This drug is not supposed to be combined with isosorbide mononitrate, nitrates and isosorbide dinitrate or any other medications of the kind. Make sure you always talk to a qualified health care professional before you take Viagra. This is necessary, as you will be able to learn more about the options you have and how efficient Viagra is expected to be for you. The following medications are supposed to be discussed in case you are already taking them or are planning to start taking them along with Viagra: certain barbiturates, anticoagulants, medications for high blood pressure, alpha blockers, other medications for erectile dysfunction, seizure medications, cimetidine, HIV protease inhibitors, efavirenz, erythromycin, nevirapine, certain antifungals, beta blockers, and some other ones. Viagra is usually taken an hour before you are planning to have sex. It is very important that you talk to your doctor about any contraindications you have.