I have been taking .75 Synthroid for years which kept my thyroid level at .1. I felt great and was at normal weight. I quit smoking and my system seemed to just go haywire. My thyroid level went up to 3.3 and I have gained a lot of weight, tiredness, trouble breathing since. It has been 1 1/2 yrs. since I quit smoking and thought everything would settle down but it hasn't. My doctor says 3.3 is perfect. Does smoking effect the thyroid that much?