Brought to you by Mary Shomon Your Thyroid Guide
Public Citizen's Correction Letter, Being Sent by Betty Blount & Peter Lurie, September 25th -- September 25, 2003
For background, read:
September 25, 2003
Dear Correspondent:
We are writing to correct an unintended error in our recent correspondence. In that correspondence, we erroneously stated that desiccated thyroid USP does not require a prescription and implied that it is regulated as a dietary supplement. In fact, the drug is a prescription product under U.S. Food and Drug Administration (FDA) regulations. We regret the error.
Nonetheless, we stand by our assertion that desiccated thyroid should not be used in the management of hypothyroidism. Our reasoning depends on an understanding of thyroid hormone function in the body. The most active thyroid hormone, T3, is formed by removing one of four iodine atoms from a precursor molecule called T4 (also called levothyroxine, the ingredient in most thyroid replacement formulations). Because T4 is converted to T3 at a predictable rate, the FDA regulates T4 (also a prescription drug) by measuring the exact amount of T4 in the pill. In contrast, desiccated thyroid is formulated from ground pig thyroid gland, and thus has a mixture of active and inactive thyroid molecules: T4, T3, and even molecules with only one or two iodine atoms, which have essentially no activity. Because desiccated thyroid is an unpredictable mixture of these compounds, the FDA only requires that iodine content (as opposed to hormone content) be measured. Thus, there is no way of knowing if the iodine present is in an active or inactive form, and therefore what the compound’s biological activity will be. We cannot recommend products whose biological activity we cannot reasonably predict.
The result is that one cannot know with sufficient certainty how much active thyroid hormone will be released into the blood and patients can become either hypothyroid from insufficient hormone or toxic from too high a dose of the hormone. There could be big variations in biological activity not only between T4 preparations and desiccated thyroid, but also between bottles of desiccated thyroid.
We hope this clarifies this issue and regret our error.
Sincerely,
Betty Blount, RN
Volunteer
Public Citizen
Peter Lurie, MD, MPH
Deputy Director
Public Citizen’s Health Research Group
IMPORTANT NOTE FROM MARY SHOMON: Please read my September 25, 2003 point-by-point rebuttal and response to this letter now.
