Your metabolism is controlled by the action of your thyroid gland and thyroid hormones, which regulate how fast or slow your other body organs work. When your thyroid gland is overactive, it produces too much thyroid hormone, which results in symptoms of hyperthyroidism, or Grave's disease. When your thyroid is sluggish, not enough thyroid hormone is produced, resulting in hypothyroidism. Certain herbs can affect your thyroid gland and hormones. Some are beneficial for hyperthyroidism but can worsen the symptoms of hypothyroidism, and vice versa. Never take any herbs that affect thyroid function without consulting your physician.
Bladderwrack, or Fucus vesiculosus, is a brown seaweed found growing in the cool, northern shores of the Atlantic and Pacific coasts. Bladderwrack contains a high concentration of iodine and is used to treat underactive thyroid, or hypothyroidism, caused by an iodine deficiency, according to the University of Michigan Health System. However, taking bladderwrack can be harmful if you have an overactive thyroid gland, because it can cause an overload of iodine. Also, extended use of bladderwrack may cause a goiter, or over-sized thyroid gland, to form as a result of high iodine content. Use bladderwrack only under the direct supervision of your doctor.
Fenugreek is the hard, brownish-red seed of the Trigonella foenum-graecum plant, which is used as both an herb and a culinary seasoning. In India, fenugreek is often used to lower high blood glucose levels associated with type 1 and type 2 diabetes. It is also used to stimulate lactation in nursing women. However, avoid fenugreek if you have either an underactive thyroid or overactive thyroid gland. Phyllis A. Balch, author of "Prescription for Herbal Healing," says that fenugreek can alter the levels of your thyroid hormones. Consult your doctor before taking fenugreek if you have thyroid problems.
Astragalus is a bushy legume whose long, firm roots are used in herbal preparations. Astragalus appears to enhance some immune functions while suppressing others. It has many medicinal uses, including heart disease, heart failure, atherosclerosis, bladder infections and immune disorders, such as rheumatoid arthritis and lupus. If you are in the early stages of hypothyroidism, avoid herbs that stimulate the immune system, such as astragalus, to maintain any remaining thyroid function. If you have any type of thyroid disease, don't take any herbs, including astragalus, without discussing it with your health care provider.
Soy isoflavones are a concentrate derived from the soybean that contain beneficial compounds, including genistein and daidzein. In general, soy isoflavones have estrogen-like properties and are used for atherosclerosis, Alzheimer's disease, symptoms of menopause and osteoporosis. However, you should not take soy isoflavones if you have thyroid disease. According to Balch, soy isoflavones can interfere with your body's ability to use thyroid hormones effectively. Use soy isoflavones only under the supervision of your physician.