Most of what I know about Effexor says if anything if decreases sex drive. It's a horrible side effect for many. Patients feel like they have to choose between treating a mental health condition or a satisfying sex life.

One thought I have is that perhaps the Effexor is effectively treating your depression or other conditions that may have decreased your sex drive. So it's not the Effexor that's increasing your drive but the fact that your mental health conditions are being treated.

Here's an article you may find of interest:
http://www.mayoclinic.com/health/ant...ssants/MY00197

Just my $0.02...