A 40-year-old female is diagnosed with primary hypothyroidism and started on levothyroxine 75 mcg daily. She returns for a follow-up visit. When should her thyroid-stimulating hormone (TSH) level be rechecked to assess the adequacy of treatment?

✓ Correct Answer: Option B

The half-life of levothyroxine is approximately 7 days. It takes about 5-6 half-lives (5-6 weeks) to reach a new steady state in the body. Therefore, TSH should be rechecked around 6 weeks after starting or changing the dose to assess efficacy.