depression
"I started taking Zoloft over a year ago, and at first it improved my mood 90%.  That was senior year of high school.  Then I started college, my increased stress also had me increase my dose from 50-75 mg.  Since then I have gained 45 lbs, had a severe decrease in my sex drive, and upon increasing to 100mg, have been so apathetic and just not wanting to do anything.  I am 19.  Shouldn't really happen for me.  For some people it works great, for me, I'm just going cold turkey from here out."