The thyroid hormones T3 and T4 are produced in the thyroid gland. Of the two, T3 is the active form. In order for the body to utilize T4, it must first be converted into T3. While the thyroid does produce some T3, the body converts T4 into the rest of the T3 it needs, mostly in the liver but also to some degree in the kidneys and bodily tissues. Among the herbs that may increase the body's conversion of T4 to T3, says naturopathic physician Dr. Frank Aieta, N.D., are guggul, ashwaganda and coleus. Do not use any herbs to treat hypothyroidism or otherwise support the liver or thyroid without first consulting with your doctor.
Also known as "underactive thyroid," hypothyroidism is a disorder of the thyroid gland in which the thyroid fails to produce enough T4 and T3 thyroid hormones. If you exhibit symptoms of hypothyroidism and your lab results from your doctor report that your T4 levels are normal, this may indicate that your body is having a problem converting T4 to T3.
Herbs that promote healthy liver function are called hepatics. Among the most effective hepatics, according to David Hoffman in "The New Holistic Herbal," are balmony, barberry, black root, blue flag, centaury, dandelion, fringetree, golden seal, mountain grape, wahoo and wild yam.
According to naturopathic physician Dr. Michael Stadtmauer, N.D., guggul, or Commiphora mukul, promotes conversion of T4 to T3. Acting on both the thyroid and the liver as well as reducing lipid peroxidation, or free radical damage to fats, guggul is believed to increase T3 conversion in part by protecting the liver against free radicals. The University of Maryland Medical Center advises taking a standardized extract of 250 to 300 mg of guggul three times per day to support thyroid activity.
Dr. Stadtmauer also lists the Ayurvedic herb ashwaganda as a known promoter of T4 to T3 conversion. The mechanism for this support is believed to be much the same as for guggul, warding off free radicals from the liver and thereby improving overall liver function, including that of converting T4 to T3. According to the Langone Medical Center at New York University, standard dosage is three times daily taking 1-2 grams of ashwaganda root boiled in water or milk for about 15 minutes in water or milk.
Coleus forskohlii is an Ayurvedic herb native to the subtropics of India, Burma and Thailand. It was found in the mid-'80s to increase thyroid hormone production and secretion into the bloodstream. The University of Maryland Medical Center suggests a 50 to 100 mg standardized extract two or three times daily for thyroid support.