One dose of tadalafil taken as needed for sexual activity can remain effective for up to 36 hours, however peak concentration of tadalafil in the bloodstream usually occurs between 30 minutes and 6 hours with a median time of 2 hours. Since the effectiveless of tadalafil lasts for a long time, it can be taken well in advance to allow for more spontaneous sexual activity over the course of a day or night.