Cialis (tadalafil) is one of the three most popular medications for the treatment of male impotence, more precisely defined as erectile dysfunction. If compared to the other two, however, Cialis can provide you with the longest period of efficiency 0- up to 36 hours, which gave some people the reason to call it "the weekend pill". Cialis is recommended for people with real problems, which means you are not supposed to be taking it if you have temporary problems that may be related to some stress at work etc. Talking to your doctor before starting the treatment is recommended. You can discuss any contraindications you may have to avoid dangerous health effects. Being allergic to tadalafil will probably make it impossible for you to take Cialis, as otherwise allergic reaction is most likely to happen again. Also you may want to mention any of the following health condition you have or used to have that can affect the dose you are prescribed and make your doctor monitor your condition carefully for any side effects that may be dangerous: hypertension, retinitis pigmentosa, bleeding disorder, kidney disease, blood cell disorder, a history of stroke, stomach ulcer, liver disease, heart rhythm problems, congestive heart failure, a history a heart attack, hypotension, chest pain, or heart disease.