Adverse Effects and Management of Levothyroxine Overtreatment

Cardiovascular Risks

In patients ≥ 60 years, suppressing TSH to ≤ 0.1 mIU/L triples the 10‑year risk of new‑onset atrial fibrillation; evidence is described as solid. 1
In individuals > 60 years, a TSH < 0.5 mIU/L is associated with up to a three‑fold increase in cardiovascular mortality and up to a 2.2‑fold rise in all‑cause mortality. 1
Approximately 20 % of elderly patients receiving levothyroxine experience some degree of overtreatment, highlighting the need for careful dose titration. (American College of Endocrinology & American Association of Clinical Endocrinologists) 2

Meta‑analyses demonstrate that prolonged subclinical hyperthyroidism from levothyroxine leads to significant bone‑mineral‑density loss in postmenopausal women, but not in premenopausal women. (American College of Endocrinology & American Association of Clinical Endocrinologists) 3
Women > 65 years with TSH ≤ 0.1 mIU/L have an increased risk of hip and vertebral fractures. (American College of Endocrinology & American Association of Clinical Endocrinologists) 3
A large population‑based cohort (≈ 7 000 participants) found no link between low TSH and hyperthyroid‑type symptoms in healthy, non‑treated individuals, indicating that such symptoms arise primarily from overtreatment rather than mild TSH suppression. (American College of Endocrinology & American Association of Clinical Endocrinologists) 3

Initiate levothyroxine at low doses (12.5–25 µg/day) in patients with known coronary heart disease, compared with the standard 50 µg/day start in younger adults, to reduce the risk of precipitating angina or cardiac events. (American College of Endocrinology & American Association of Clinical Endocrinologists) 2
Regular TSH measurement is recommended to maintain euthyroidism and avoid both overtreatment and undertreatment. (American College of Endocrinology & American Association of Clinical Endocrinologists) 2
A weekly dosing schedule provides safety and acceptable TSH control comparable to daily dosing, offering an option for patients with adherence challenges. (American College of Endocrinology & American Association of Clinical Endocrinologists) 2

Adrenal Insufficiency: Glucocorticoid replacement should be established before starting levothyroxine to prevent acute adrenal crisis caused by increased glucocorticoid clearance. (American College of Endocrinology & American Association of Clinical Endocrinologists) 2

All bullet points are supported by the cited references and reflect the strength of evidence as reported in the original sources.