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    Can melatonin make hypothyroidism worse?

    The sources reviewed do not establish that ordinary melatonin use predictably worsens hypothyroidism, but they also do not justify a blanket safety assurance. Thyroid-related melatonin research includes animal studies that cannot determine a human treatment plan. Review the cause of the thyroid disorder, medicines and sleep symptoms with a clinician.

    Read the evidence ↓

    Supplement Science Insights Editorial Team

    Published September 23, 2026

    Animal thyroid findings are not a human prescription

    A review of melatonin, hypothyroidism and gonadal development discusses changes in thyroid hormones in rats. Such findings do not show that melatonin treats human hypothyroidism, nor do they establish that it inevitably lowers thyroid function in people. Species, doses and disease models matter. [1]

    The cause of hypothyroidism changes the discussion

    NHS advises discussing melatonin with a clinician in autoimmune conditions. That is relevant when a thyroid disorder is autoimmune, but is a precaution requiring assessment rather than proof that every person with hypothyroidism will be harmed. Include kidney or liver disease and other medicines in the review. [2]

    Keep thyroid treatment and monitoring consistent

    Levothyroxine replaces deficient thyroid hormone, and its dose is guided by clinical assessment and blood tests. Do not lower, stop or move it unpredictably to accommodate an optional sleep supplement. Tiredness and sleep complaints may need review of thyroid control or another cause. [3]

    Assess a change rather than assume its cause

    Imagine fatigue worsens after starting melatonin. Daytime drowsiness is one possible explanation; worsening thyroid function is not established by symptoms alone. Report the timing and products and arrange appropriate review rather than changing thyroid medicine yourself. [4][3]

    Hypothetical example — separate thyroid questions
    IssueAssessment
    Rat hormone findingNot a human treatment rule
    Autoimmune diseaseDiscuss before melatonin
    Levothyroxine doseGuided by monitoring
    New fatigueSeveral possible causes
    Can melatonin make hypothyroidism worse? — original article outline diagram
    Original editorial diagram of this article’s sections; no product photograph or clinical finding is depicted.

    Sources for this article

    1. Melatonin on hypothyroidism and gonadal development in rats: a review.
      Source consulted: 2026-09-21. This is a reference resource, not a claim that we conducted the studies or tested a product.
    2. Who can and cannot take melatonin - NHS
      Source consulted: 2026-09-21. This is a reference resource, not a claim that we conducted the studies or tested a product.
    3. Levothyroxine: a medicine for an underactive thyroid (hypothyroidism) - NHS
      Source consulted: 2026-09-21. This is a reference resource, not a claim that we conducted the studies or tested a product.
    4. Common questions about melatonin - NHS
      Source consulted: 2026-09-21. This is a reference resource, not a claim that we conducted the studies or tested a product.