I was started on synthroid because i couldn't lose weight and my hair was getting thin. however since going on it 7 months ago i have gained weight even though i exercise and do a 1200 calorie diet. can i just stop this med without serious side effe?

I would consult with an endocrinologist. Generally synthroid is prescribed for hypothyroidism . Were you hypothyroid ? Thyroid supplements should not be given solely to lose weight. If you are truly hypothyroid you may need to stay on the thyroid supplments..

Weight gain almost certainly not related to low thyroid if meds normalized. Get the app Cronometer and enter all you eat and drink and exercise. Look at calories that go in -calories that go out (exercise) and adjust so in is greater lower that out and weigh will go down. Eating about 500 calories per day less than you do now should give you about 1 lb loss per week. 1000 less ,down 2 lbs etc.