Viagra (sildenafil citrate) can be used for patients diagnosed with erectile dysfunction - a commonly diagnosed condition characterized by the complete or partial inability of a male patient to get or maintain an erection hard enough to have sex. Viagra has been specially designed for males and is never supposed to be taken by females, as it is unlikely to help them get any benefits. You are not supposed to take Viagra if you are already using anticoagulants, HIV protease inhibitors, beta blockers, medications for high blood pressure, alpha blockers, certain antifungals, other medications for erectile dysfunction, erythromycin, efavirenz, seizure medications, nevirapine, certain barbiturates, or cimetidine, as those drugs can cause interactions and affect the success of your treatment. There are other medications you are not supposed to combine with Viagra because of the risk of suffering from interactions. Make sure you read the label of this medicine carefully if purchasing it online, and never share your dose with other people. These days Viagra can be purchased online, and more people do this, as it saves them a lot of time and money.