If you take syntroid, does the normal thyroid gland stops producing hormone?

Thyroid hormone. Yes. An abnormal thyroid (Eg. Graves, multinodular goiter) may continue to make thyroid hormone even while taking synthroid (thyroxine).
It depends. it really depends how much we are taking,the medication will suppress the thyroid, the question is the suppression partial,or complete. and that dependson the dose.