Evaluation of Two Over-the-Counter Natural Thyroid Hormone Preparations in Human Volunteers

OBJECTIVE: To determine the pharmacologic activity of over-the-counter (OTC) thyroid preparations.DESIGN: In vitro analysis and a prospective, crossover study in vivo.SETTING: Tertiary care center.PARTICIPANTS: Two healthy adult volunteersINTERVENTION: Three OTC preparations (Thytrophin PMG [bovine thyroid PMG extract], Thyro Forte [thyroid lyphogland concentrate with synergistic complex], and Thyro Complex [thyroid lyophilized gland concentrate with synergistic complex]) were analyzed in vitro. Volunteers were administered two times the manufacturer's maximum recommended daily dose of either Thytrophin PMG or Thyro Forte for one week, washed out for four to five weeks, and crossed over to receive the opposite tablet preparation for an additional week.MAIN OUTCOME MEASURES: The triiodothyronine (T3) and thyroxine (T4) contents of OTC preparations were measured by HPLC. Vital signs, serum total and free T4, total T3, thyroid stimulating hormone, thyroxine binding globulin, thyroglobulin, and general chemistry tests (including glucose and cholesterol) were monitored before, during, and between administration of the products.RESULTS: HPLC analysis of the three OTC preparations showed no T4but did show possible T3in two of these products. We found no definite clinical or laboratory evidence of thyroid hormone excess with either product.CONCLUSIONS: Healthcare professionals should advise against the use of these scientifically unsound and relatively expensive OTC thyroid preparations, of which the therapeutic efficacy is unknown.