NutriStack
Iron Bisglycinate and Levothyroxine, timing-sensitive.
Iron bisglycinate contains elemental iron and should be handled like other oral iron supplements around levothyroxine. Iron can bind thyroid hormone in the gut and lower absorption, which may raise TSH and bring back hypothyroid symptoms. The strongest human data are with ferrous sulfate, but the same timing precaution is appropriate for bisglycinate because the interacting component is iron.
One pair, every claim cited. The two substances, the type, the mechanism, the recommendation, and the primary literature.
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At a glance
- Substances
- Iron Bisglycinate and Levothyroxine
- Pair type
- Timing Sensitive
- Evidence (highest tier)
- Moderate
- Source citations
- 3 sources
- Stack Score effect
- −5 to your Stack Score (per scored timing-sensitive row).
- Scope
- Supplement × Prescription
- Last verified
- May 30, 2026
Timing Sensitive · Moderate evidence
Timing Sensitive
What is happening. Iron bisglycinate contains elemental iron and should be handled like other oral iron supplements around levothyroxine. Iron can bind thyroid hormone in the gut and lower absorption, which may raise TSH and bring back hypothyroid symptoms. The strongest human data are with ferrous sulfate, but the same timing precaution is appropriate for bisglycinate because the interacting component is iron.
Mechanism. Ferrous and ferric iron can form poorly absorbed iron-thyroxine complexes in the intestinal lumen. Reduced levothyroxine bioavailability can lead to compensatory TSH elevation and higher dose requirements.
Recommendation. Take levothyroxine on an empty stomach with water, and take iron bisglycinate at least 4 hours later. Recheck thyroid labs after starting, stopping, or substantially changing iron supplementation.
Minimum separation. 240
Sources (3)
- Campbell NRC, Hasinoff BB, Stalts H, Rao B, Wong NCW. Ferrous sulfate reduces thyroxine efficacy in patients with hypothyroidism. Ann Intern Med. 1992;117(12):1010-1013. PMID 1443969
- Shakir KM, Chute JP, Aprill BS, Lazarus AA. Ferrous sulfate-induced increase in requirement for thyroxine in a patient with primary hypothyroidism. South Med J. 1997;90(6):637-639. PMID 9191742
- Wiesner A, Gajewska D, Pasko P. Levothyroxine Interactions with Food and Dietary Supplements-A Systematic Review. Pharmaceuticals (Basel). 2021;14(3):206. PMID 33801406
Stack Score
How this pair moves the number.
Effect on the composite score
If both Iron Bisglycinate and Levothyroxine are in the same stack, this pair applies −5 to your Stack Score (per scored timing-sensitive row).
The full algorithm, the clamping rules, and four worked stacks are documented at /methodology/stack-score.
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