Erectile dysfunction affects millions of men every year with causes ranging from psychological to purely physical. Viagra Cialis and Levitra are prescription PDE inhibitors that are supposed to be taken when needed by patients diagnosed with erectile dysfunction These medicines differ in the period of time during which they remain efficient with Cialis lasting for p to 36 hours. It’s strongly recommended to visit a doctor before taking either of these drugs as you will need professional advice and examination before making up your mind about the best method of treatment. Firstly, you will be able to learn whether your condition is actually erectile dysfunction and requires treatment with oral medications (for some patient lifestyle modification is sufficient). Secondly, if you do have to take this medicine your doctor will make sure none of the health conditions you have interfere with the treatment and that your treatment is not affected by any other drugs you are currently taking. For instance, you must not combine any nitrate-based medicines with PDE inhibitors, as a sudden drop in blood pressure is likely to occur.