What can I do to reduce a thyroid goiter?

Cause?? If a goiter is the result of anti-thyroid antibodies and your thyroid function is normal, there isn't much to be done. It will eventually go down on its own as long as thryoid function is kept normal. If from over/under active thyroid, medication may help. Multinodular goiters are more complicated and may need surgery. Other reasons also, so please discuss cause/treatment options with doctor.