When on Lithium, it is definately a must to have a "before and after" thyroid function blood work, plus tests should be done once to twice a year,minimum. Doctors prescribing this med. do that.
I also suggest if a person hasn't had such bloodwork, and feel runned down,depressed,etc. to have it done. I say this because so often the symptoms are very much like the symptoms of depression, and many GP's hand out scripts so often for AD's, when actually it was the patient's thyroid function/dysfunction causing the depression and/or fueling the depression.