How do you know if your levothyroxine dose is right?
Last updated September 3, 2026.
Two witnesses: your symptoms and your TSH blood test - checked 6 to 8 weeks after any dose change (TSH needs that long to settle) and yearly when stable, per the NHS. Underdose feels like your old hypothyroid self: fatigue, weight creep, cold intolerance, constipation, fog. Overdose mimics hyperthyroidism: racing or irregular heartbeat, shakiness, sweating, anxiety, diarrhea, poor sleep, headaches, weight loss. The fakes: taking it with food, coffee, or other medicine (all blunt absorption - empty stomach, 30 to 60 minutes before first meal or caffeine), calcium and iron within 4 hours, and biotin supplements, which distort the lab itself. Never self-adjust on a good or bad week - symptoms plus TSH, read together, drive changes. Pymander is a free AI doctor, 24/7 by text, and can help you read the pattern.
What to do
- Empty stomach, 30 to 60 minutes before breakfast or coffee: every day.
- Calcium and iron 4 hours away: they bind the dose.
- Test 6 to 8 weeks after changes: earlier results mislead.
- Stop biotin before the draw: it bends the TSH number.
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