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Which thyroid hormones contain iodine?

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The two thyroid hormones that contain iodine are thyroxine (also known as $T_{4}$ or tetraiodothyronine) and triiodothyronine (also known as $T_{3}$ ).12

These hormones are the only biologically active substances in the body that contain iodine, and they cannot be synthesized without it. Their chemical composition is as follows:1

Thyroxine ( $T_{4}$ ): Contains four iodine atoms.1
Triiodothyronine ( $T_{3}$ ): Contains three iodine atoms.1

Both hormones are synthesized from tyrosine, an amino acid, within the thyroid gland. While the thyroid gland produces the majority of the body's thyroxine, most triiodothyronine is produced in peripheral tissues through the action of enzymes called deiodinases, which remove one iodine atom from thyroxine.1