My son has experienced the exact same thing. Since he is only 16 we know its not just because he's getting "Older"! It actually is a known side effect of Zoloft although it is fairly rare, it's called "Telogen Effluvium" and sometimes lowering your dose may cause it to stop. But, if that doesn't help then you might need to choose. Switch to another antidepressant or deal with thin hair.