Discontinuation of Low-Dose Levothyroxine in Older Adults With Subclinical Hypothyroidism

The goal of this clinical trial is to learn whether low-dose levothyroxine can be safely discontinued in adults aged 65 years or older who are taking levothyroxine for subclinical hypothyroidism. The study will also evaluate the cost-effectiveness of discontinuing levothyroxine. The main questions it aims to answer are: * Does discontinuing levothyroxine result in no clinically meaningful worsening of thyroid-related symptoms compared with continuing levothyroxine? * What are the effects of discontinuing levothyroxine on quality of life, tiredness, cognition, thyroid hormone levels, lipid levels, weight, and adverse events? * Is discontinuing levothyroxine cost-effective compared with continuing treatment? Researchers will compare participants who discontinue levothyroxine and receive placebo with participants who continue their current dose of levothyroxine to determine the effects of levothyroxine discontinuation. Participants will: * Complete a 2-week run-in period during which they continue their usual levothyroxine and record their medication use. * Eligible participants will be randomly assigned to either continue their current dose of levothyroxine or receive a matching placebo for 6 months. Participants, their clinicians, and study investigators will not know which treatment they are receiving during the study. * Complete study assessments at baseline, approximately 2 months, and 6 months. Assessments will include blood tests, measurements such as body weight, questionnaires about thyroid-related symptoms and quality of life, and assessments of cognition and other health outcomes.