What is hypothyroidism?
Hypothyroidism is under-production of thyroid hormone, most often from autoimmune destruction (Hashimoto's). It commonly presents with fatigue, cold intolerance, weight gain, and constipation.
Full answer
Hypothyroidism is diagnosed by elevated TSH with low free T4 (overt) or elevated TSH with normal free T4 (subclinical). The dominant cause in adults is autoimmune thyroiditis (Hashimoto's), often with positive TPO antibodies. Symptom expression varies and biomarker thresholds are debated, particularly in the subclinical zone. Within oMeds review, thyroid status is interpreted with TSH, free T4, free T3, reverse T3, and TPO antibodies in context, never with TSH alone. Replacement decisions consider symptoms, biomarker trajectory, and provider judgment.
Educational. Not a substitute for individualized provider review.
- TSH — Primary source · oMeds
- Reviewed by Dr. Laura Purdy, MD, MBA · Clinical Director, oMeds · Last reviewed 2026-05-29