This looks like it could actually be the opposite: more non-aromatizable steroids = less TBG = more free T3?
Or am I incorrectly assuming that (like with AAS and SHBG) less TBG = more free T3?
Acta Clin Belg. 2013 Jan-Feb;68(1):65-7.
Methyltestosterone-induced transient hyperthyroidism in a hypothyroid patient.
Krysiak R, Okopien B.
In this paper we report different effects of methyltestosterone administration on thyroid function in two twin brothers, one of whom suffered from hypothyroidism, while the other was apparently healthy.
Methyltestosterone, which is a non-aromatisable androgen, resulted in a marked reduction of thyroxine-binding globulin (TBG), irrespectively of the patient's hormonal status, while the impact on free thyroid hormones depended on baseline thyroid function. Our research shows that a possibility of the use of non-aromatisable androgens or other drugs affecting TBG levels should be taken into consideration in all hypothyroid patients receiving levothyroxine, in whom thyroid hormone status suddenly changes without any apparent reason.
PMID: 23627199
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Best Pract Res Clin Endocrinol Metab. 2009 Dec;23(6):769-80. doi: 10.1016/j.beem.2009.06.005.
Sex steroids and the thyroid.
Tahboub R, Arafah BM.
Thyroid function is modulated by genetic and environmental causes as well as other illnesses and medications such as gonadal or sex steroids. The latter class of drugs (sex steroids) modulates thyroid function. Gonadal steroids exert their influence on thyroid function primarily by altering the clearance of thyroxine-binding globulin (TBG).
While oestrogen administration causes an increase in serum TBG concentration, androgen therapy results in a decrease in this binding protein. These effects of gonadal steroids on TBG clearance and concentration are modulated by the chemical structure of the steroid being used, its dose and the route of administration. Despite the gonadal steroids-induced changes in serum TBG concentrations, subjects with normal thyroid glands maintain clinical and biochemical euthyroidism without changes in their serum free thyroxine (T4) or thyroid-stimulating hormone (TSH) levels. In contrast,
the administration of gonadal steroids to patients with thyroid diseases causes significant biochemical and clinical alterations requiring changes in the doses of thyroid medications. Similarly, gonadal steroid therapy might unmask thyroid illness in previously undiagnosed subjects. It would be prudent to assess thyroid function in subjects with thyroid disease 6-8 weeks after gonadal steroid administration or withdrawal.
PMID: 19942152