I am considering switching from Levitra to Cialis. Have read that Cialis has a longer half life (up to 36 hrs vs. 5-7 hrs.). Anyway, I have tried extending Levitra's half-life by taking a second dosage a few hours later, but no matter what, the max effects still really fade off 5-7 hours after the initial dosage. Wondering if anyone knows why this might be... and why a second dose would not extend the effects? Just helps with planning.