What happens in treatment if / when you max out on thyroid rx? I am female, recently on 137 mcg of levothyroxine (age 56). My older sister is on 75 mcg. I am also diabetic type 2. All of this in the family, and mine (both conditions) occurred around 4 years ago. What happens after one reaches the max 300 mcg of levothyroxine? (I hope not to reach that). My diabetes is well under control, but hypothyroid condition was detected at same time, and there’s not much I can do to control it except rx, correct?