Active ingredient: Levothyroxine (T4)

Brand Name: Levoxyl, Unithroid, Synthroid, Tirosint

Drug class: Thyroid Products

Mechanism of Action:

Levothyroxine sodium (T4) is a synthetic form of the thyroid hormone thyroxine (T4). In the body, T4 is converted to the active form, triiodothyronine (T3), which regulates metabolism. Levothyroxine binds to thyroid hormone receptors in cells, influencing gene expression and increasing metabolic activity. It is primarily used to treat hypothyroidism, where the thyroid does not produce enough thyroid hormones.

Effect on fertility biomarkers

Thyroid hormones, particularly T4, increase body temperature by stimulating metabolism and thermogenesis. Higher levels of free T4 can affect the menstrual cycle, often leading to longer cycle lengths. This is due to a prolonged follicular phase, while the luteal phase tends to remain unchanged. These changes can influence fertility and cycle tracking, particularly when basal body temperature is used as a marker..

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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.