Substances such as perchlorate, thiocyanate, and some pharmaceuticals like methimazole and propylthiouracil are well-documented TPO inhibitors. Perchlorate, often found in contaminated water sources, competes with iodine uptake in the thyroid gland, impairing TPO's ability to synthesize hormones. Similarly, thiocyanate, a byproduct of cigarette smoke, also inhibits iodine uptake.
