For how long does effexor (venlafaxine) cause insomnia?

Short term: There are at least three effects that venlafaxine (effexor) has on sleep - it has a short term effect increasing agitation and insomnia that lasts usually only a few days, it has a long term effect improving sleep by treating depression (which has a big negative effect on sleep), and it has a small long term effect reducing rem or dream sleep. For most people #2 is the most important.