10 mg sounds like a relatively low dose, and 4 months is a long time to go without titrating upwards. 25 mg of Zoloft is also a low dose, upping the dose of Zoloft might help. Assuming your son is old enough and mentally capable of making decisions for himself, the only person that can decide whether or not he can go off of medication is him. If he's young or not capable, keep consulting with the doctor/therapist, but make sure you listen to what your son has to say as well. As the above poster said, everyone is different, and I'm sure he knows himself better than anyone else.