T3’s negative effect on other hormones

Apparently some people can remain on T3-only indefinitely and actually feel fine, or certainly better than they ever did on T4 medications.  Others, however, become worse, because the high T3 levels have side effects and create imbalances in other hormones.  In men, high T3 levels will cause sex hormone binding globulin (SHBG) to rise, the production rate of estradiol to rise, and the metabolic clearance rate of estradiol to fall. [1, 52]  The net effect is higher estradiol levels, which can have a disastrous effect on men’s hormone levels. In men, a hyperthyroid state can elevate estradiol and result in gynecomastia (male breasts). [2]  Premature ejaculation seems to be a problem for hyperthyroid men, and delayed ejaculation a problem for hypothyroid men. [53]  High SHBG in men also correlates with osteoporosis and a higher fracture risk. [55]

SHBG also rises in women taking additional T3.  The metabolic clearance rate of estradiol decreases [52] and anecdotally, women have reported painful breasts on the T3-only protocol.  Women’s testosterone levels also decrease on this protocol.  This may be desirable if a woman exhibits high androgen symptoms like facial hair, infertility, etc., but undesirable if levels become too low. [54]

In women, estrogen and progesterone can also raise SHBG if taken orally [3], so if a woman is on these other hormones and following the T-3 only protocol, her system can become quite imbalanced.  Hormonal imbalance is often the cause of both physical and emotional symptoms.


1. Sonia C Dumoulin, Bertrand P Perret, Antoine P Bennet and Philippe J Caron. Opposite effects of thyroid hormones on binding proteins for steroid hormones (sex hormone-binding globulin and corticosteroid-binding globulin) in humans. European Journal of Endocrinology, 1995, Vol 132, Issue 5, 594-598.http://www.eje-online.org/cgi/content/abstract/132/5/594

2. Wayne Meikle. The Interrelationships Between Thyroid Dysfunction and Hypogonadism in Men and Boys. Thyroid. April 2004, 14(supplement 1): 17-25.http://www.liebertonline.com/doi/abs/10.1089/105072504323024552

3. Shifren, Jan L., Desindes, Sophie, McIlwain, Marilyn, Doros, Gheorghe, Mazer, Norman A. A randomized, open-label, crossover study comparing the effects of oral versus transdermal estrogen therapy on serum androgens, thyroid hormones, and adrenal hormones in naturally menopausal women. Menopause: November/December 2007 – Volume 14 – Issue 6 – pp 985-994.

52. Jaime Olivo, Gary G. Gordon, F. Rafii and A. Louis Southren. Estrogen metabolism in hyperthyroidism and in cirrhosis of the liver.  Steroids. Volume 26, Issue 1, July 1975, Pages 47-56. http://www.sciencedirect.com/science/article/pii/0039128X75900057

53. Cesare Carani, Andrea M. Isidori, Antonio Granata, Eleonora Carosa, Mario Maggi, Andrea Lenzi and Emmanuele A. Jannini. Multicenter Study on the Prevalence of Sexual Symptoms in Male Hypo- and Hyperthyroid Patients.The Journal of Clinical Endocrinology & Metabolism December 1, 2005 vol. 90 no. 126472-647.  http://www.ncbi.nlm.nih.gov/pubmed/16204360?dopt=Abstract

54. G Kazanavicius. New approach in treatment of hyperandrogenism with triiodothyronine.  Endocrine Abstracts(2004) 7  http://www.endocrine-abstracts.org/ea/0007/ea0007p174.htm

55. Lormeau C, Soudan B, d’Herbomez M, Pigny P, Duquesnoy B, Cortet B. Sex hormone-binding globulin, estradiol, and bone turnover markers in male osteoporosis.  Bone. 2004 Jun;34(6):933-9. http://www.ncbi.nlm.nih.gov/pubmed/15193539/