depression
"I was on Effexor XR for about 4 years (started at age 18, weaned off at 22). Over the years, my dosage fluctuated between 37.5 and 300 mgs. 
It helped immensely throughout the first year. I was still feeling lethargic and such, but no longer had suicidal thoughts. 
The only side effects I had were ones that appeared when I'd miss a dose. Night sweats, weird dreams, headaches. Annoying, but basically harmless.
After three years of being on this medicine, I realized it was no longer doing things for me that I couldn't do myself. I was supposed to be taking 37.5 mgs daily, but weaned myself off of it over a course of several months (check with your doctor first). I had little to no withdrawal symptoms and no major signs of a returning depression."