From the FDA Drug Label
Thyroid Abnormalities: Euthyroid goiter and/or hypothyroidism (including myxedema) accompanied by lower T3 and T4. Iodine 131 uptake may be elevated. Previously existing underlying thyroid disorders do not necessarily constitute a contraindication to lithium treatment; where hypothyroidism exists, careful monitoring of thyroid function during lithium stabilization and maintenance allows for correction of changing thyroid parameters, if any Where hypothyroidism occurs during lithium stabilization and maintenance, supplemental thyroid treatment may be used.
Lithium Effects on TSH Levels: Lithium can cause hypothyroidism, which is accompanied by lower T3 and T4 levels and may require supplemental thyroid treatment.
- TSH Level Increase: Although the exact effect of lithium on TSH levels is not explicitly stated, it can be inferred that lithium may increase TSH levels as a result of causing hypothyroidism.
- Management: Careful monitoring of thyroid function is necessary during lithium treatment, and supplemental thyroid treatment may be used if hypothyroidism occurs 1, 1.
From the Research
Lithium commonly increases Thyroid Stimulating Hormone (TSH) levels, potentially leading to hypothyroidism in patients on long-term treatment. This occurs because lithium inhibits thyroid hormone release, interferes with iodine uptake, and affects thyroid autoimmunity 2. The most recent and highest quality study, published in 2020, highlights the importance of monitoring thyroid function in patients on lithium therapy, with recommendations for baseline and regular measurements of TSH, free thyroid hormones, and antithyroid peroxidase and antithyroglobulin antibodies 2.
Key Points to Consider:
- Lithium's effect on the thyroid gland is complex, involving inhibition of thyroid hormone release, alteration of thyroglobulin structure, and reduction of iodine uptake 2.
- Regular monitoring of thyroid function is crucial, with baseline measurements before starting lithium and follow-up testing at 6- to 12-month intervals for long-term therapy 2.
- If subclinical hypothyroidism develops, monitoring should increase to every 2-3 months to watch for progression, and levothyroxine replacement therapy should be initiated if overt hypothyroidism occurs or TSH exceeds 10 mIU/L 3.
- Typical starting doses of levothyroxine are 25-50 mcg daily, adjusted every 6-8 weeks based on TSH levels, with a target TSH of 0.5-3.5 mIU/L 4.
Management and Recommendations:
- Continuing lithium while adding thyroid replacement therapy is the standard approach, allowing patients to maintain mood stability while addressing thyroid dysfunction 3.
- Lithium treatment should not be discontinued solely due to thyroid abnormalities, as the psychiatric benefits often outweigh these manageable side effects 3.
- Patients should be referred to an endocrinologist if TSH concentrations are repeatedly abnormal, or if goiter or nodules are detected 3.