Viagra (sildenafil citrate) is a drug that you may need to be taking if you have been diagnosed with erectile dysfunction and are unable to perform sexually without this kind of help. Viagra works by stimulating more powerful blood flow to the tissues of your penis therefore making it possible to get an erection and have sex. This medicine has been specially designed for males and is not supposed to be taken by female patients. You will always need to make sure you take Viagra as prescribed, or according to the instruction this medicine comes along with (in case you purchased Viagra online). Your doctor will tell you about any medications Viagra is not supposed to be combined with, such as HIV/AIDS medicines, imatinib, conivaptan, antifungals, rifampin, enoxacin, antidepressants, heart or blood pressure medications, bosentan, cimetidine, diclofenac, isoniazid, antibiotics, or any other ones of the kind. In case of buying Viagra online, you will be able to get a free consultation of a doctor (in most good pharmacies provided free of charge). Therefore, always make sure you get as much information as possible, and only then take Viagra. The dose you will need to be taking will depend on a number of factors, such as your health condition, how severe your erectile dysfunction is and a number of other ones.