Hi there, Thank you for your question. I personally think that your weight gain was because of the very fact that you were hypothyroid i.e. you had less thyroid hormone in your body than required. On thyroxine, once your TSH returns back to normal you should lose your weight. Thyroxine will help you lose weight. Additionally I would also recommend that you keep a check on your diet and do regular exercise to help with your weight loss. There is no other specific precautions other than taking your medications regularly, diet and exercise along with checking your TSH every six to eight weeks until it is in the desired range. Kindest Regards