Why T4-only medication often fails
Synthroid (levothyroxine) is T4. The active hormone is T3. Conversion depends on selenium, zinc, iron, cortisol balance, and a healthy liver and gut. If any of those are off, T4 converts to reverse T3 instead — and reverse T3 blocks the active hormone from working.
The full thyroid panel you actually need
- TSH
- Free T4
- Free T3
- Reverse T3
- TPO antibodies
- Thyroglobulin antibodies
- Plus: ferritin, vitamin D, selenium, B12, cortisol rhythm.
