I am on a low dose of Lithium and I am still getting some depression. I don't know if lithium can cause it though. It is my understanding that too many benzo's may. I take those too, but only as needed...so i am not suspicious of them causing my depression. If your son takes them daily, maybe ask your sons psychiatrist (pdoc) his/her thoughts. Either way, it may be a good idea just to inform the pdoc of what is happening in case your sons meds need a little tweeking. I hope you find the info you need!