In a woman with stable hypothyroidism on levothyroxine, does the levonorgestrel‑releasing intrauterine device (Kyleena) affect thyroid function or require adjustment of levothyroxine dose?

Kyleena IUD and Hypothyroidism: No Clinically Significant Interaction

The levonorgestrel-releasing intrauterine device Kyleena does not affect thyroid function or require levothyroxine dose adjustment in women with stable hypothyroidism. The systemic levonorgestrel exposure from Kyleena is minimal (4-13% of oral contraceptive levels), and there is no established pharmacological mechanism by which progestin-only contraceptives alter thyroid hormone metabolism or levothyroxine requirements 1.

Systemic Hormone Exposure with Kyleena

• Kyleena releases levonorgestrel locally into the uterine cavity with minimal systemic absorption, resulting in systemic exposure that is only 4-13% of that seen with combined oral contraceptives 1.
• The device contains 19.5mg of levonorgestrel and releases approximately 20 µg/24 hours, with the majority of the hormone acting locally on the endometrium rather than systemically 2, 3.
• This low systemic exposure means Kyleena has negligible effects on hepatic protein synthesis, including thyroid-binding globulin (TBG) production 4, 3.

Why Estrogen-Containing Contraceptives Differ

• Estrogen-containing oral contraceptives increase hepatic production of TBG, which binds circulating thyroid hormones and can necessitate levothyroxine dose increases in women with hypothyroidism 5.
• The estrogenic component specifically stimulates liver production of various binding proteins including TBG, sex hormone-binding globulin (SHBG), and coagulation factors 5.
• Progestin-only methods like Kyleena do not have this estrogenic effect on hepatic protein synthesis 1.

Clinical Management Approach

No Routine Monitoring Required

• Continue current levothyroxine dose without adjustment when initiating Kyleena in women with stable hypothyroidism on levothyroxine 6.
• Maintain the standard annual TSH monitoring schedule (every 6-12 months) that is already recommended for patients on stable levothyroxine therapy 6.
• No additional thyroid function testing is needed specifically due to Kyleena insertion 6.

When to Check Thyroid Function

• Only recheck TSH if the patient develops new hypothyroid symptoms (fatigue, weight gain, cold intolerance, constipation) or hyperthyroid symptoms (palpitations, tremor, heat intolerance, weight loss) 6, 7.
• If TSH becomes abnormal during Kyleena use, investigate other causes of thyroid dysfunction rather than attributing it to the IUD 6, 7.

Evidence Quality and Guideline Consensus

• Multiple international guidelines specifically address progestin-only IUDs in the context of various medical conditions, but none identify thyroid disease as a contraindication or concern 1.
• The KDIGO 2025 guidelines for ADPKD explicitly state that "the impact of progestin-only methods (pills, injections, implants, and intrauterine devices) on PLD is not known, but the level of systemic exposure with levonorgestrel-releasing intrauterine devices is low" 1.
• The EASL 2022 guidelines note that while data on levonorgestrel IUDs and polycystic liver disease is limited, the low systemic exposure makes them a reasonable contraceptive option 1.

Special Populations

Women with Autoimmune Thyroid Disease (Hashimoto's)

• Kyleena is safe for women with Hashimoto's thyroiditis or other autoimmune thyroid conditions 1.
• The autoimmune process affecting the thyroid is not influenced by the minimal systemic progestin exposure from Kyleena 7.
• Continue standard monitoring for hypothyroidism progression, which occurs at approximately 5% per year in patients with TSH >10 mIU/L and positive anti-TPO antibodies 6, 7.

Pregnancy Planning

• Women planning pregnancy who have hypothyroidism should optimize thyroid function (TSH <2.5 mIU/L) before conception, but Kyleena itself does not interfere with this optimization 8.
• When Kyleena is removed for pregnancy planning, no thyroid-related waiting period is required, as fertility and thyroid function return immediately 4, 3.

Common Pitfalls to Avoid

• Do not confuse progestin-only IUDs with estrogen-containing oral contraceptives—the latter do affect TBG levels and may require levothyroxine dose adjustment, while Kyleena does not 5.
• Do not attribute new thyroid dysfunction to Kyleena—if TSH becomes abnormal after IUD insertion, investigate other causes such as disease progression, medication interactions (iron, calcium, proton pump inhibitors taken within 4 hours of levothyroxine), or non-adherence 6, 7.
• Do not perform unnecessary thyroid function testing solely because a patient with hypothyroidism has Kyleena inserted—this leads to overmonitoring and potential inappropriate dose adjustments based on normal TSH variability 6.

Medication Interactions That Actually Matter

While Kyleena does not interact with levothyroxine, counsel patients on actual levothyroxine interactions:

• Take levothyroxine on an empty stomach, 30-60 minutes before breakfast, and separate from iron supplements, calcium supplements, antacids, and proton pump inhibitors by at least 4 hours 6.
• These medications can reduce levothyroxine absorption by 20-50%, potentially necessitating dose increases 6.