My son is diagnosed the same. He has been on INH for 3 mos. Now for some reason the doctor says he must stay on it for 9 months total, instead of the original 6 months. INH is a medication which will (to my understanding) prevent about 80-90% of those who have the virus from becoming active. It gave my son diarehhea, so we changed the time of day he takes it and all is well. There are serious side effects that can occur, your son should educate himself on these.