Active ingredient: levothyroxine sodium (T4) and liothyronine sodium (T3)

Brand Name: Thyrolar, Liotrix

Drug class: Thyroid Products

Mechanism of Action:

Levothyroxine (T4) and liothyronine (T3) are synthetic thyroid hormones. T4 is converted into the more active T3 in the body. Both hormones regulate metabolism by binding to thyroid receptors, influencing gene expression, and increasing the production of proteins that boost metabolic activity. These hormones are primarily used to treat hypothyroidism, a condition where the thyroid gland produces insufficient thyroid hormones.

Effect on fertility biomarkers

Thyroid hormones, particularly T3, increase metabolism and promote thermogenesis, which raises body temperature. As a result, body temperature and basal body temperature (BBT) may increase in individuals taking these hormones. In terms of reproductive health, higher free T4 levels can affect the menstrual cycle, often lengthening the follicular phase while the luteal phase remains consistent. This variation in cycle length can potentially impact fertility tracking based on temperature changes.

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References:

Jacobson MH, Howards PP, Darrow LA, Meadows JW, Kesner JS, Spencer JB, Terrell ML, Marcus M. Thyroid hormones and menstrual cycle function in a longitudinal cohort of premenopausal women. Paediatr Perinat Epidemiol. 2018 May;32(3):225-234. doi: 10.1111/ppe.12462. Epub 2018 Mar 8. PMID: 29517803; PMCID: PMC5980701. https://pmc.ncbi.nlm.nih.gov/articles/PMC5980701/ Iwen, K. A., Oelkrug, R., & Brabant, G. (2018). Effects of thyroid hormones on thermogenesis and energy partitioning. Journal of Molecular Endocrinology, 60(3), R157–R170. https://doi.org/10.1530/JME-17-0319

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Disclaimer: The information provided may not include all possible interactions or side effects of medication. The effects on fertility biomarkers can vary and may depend on the dosage, how long the medication is used, the medical condition, or other factors. This database is for informational purposes only and should not replace professional medical advice, diagnosis, or treatment. Always consult your healthcare provider or a qualified health professional if you have questions about medications, fertility, or medical conditions.