AVOID FLUORIDE Some strive to use fluoride and carrageenan alcohol free toothpaste and mouthwash. It is fluorine that keeps enamel strong and not synthetic fluoride. One of the most controversial issues is the impact of fluoride on the human thyroid gland. Many people are not aware that in the first half of the 20th century, fluoride was used medically as an anti-thyroid drug, to slow down the thyroid function in hyperthyroid patients.