NutriStack
Levothyroxine and Psyllium Husk, timing-sensitive.
Fiber supplements, particularly psyllium, can bind levothyroxine in the gastrointestinal tract and reduce its absorption. Studies have shown that concurrent fiber intake can decrease levothyroxine bioavailability, potentially leading to subtherapeutic thyroid hormone levels.
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At a glance
- Substances
- Levothyroxine and Psyllium Husk
- Pair type
- Timing Sensitive
- Evidence (highest tier)
- Moderate
- Source citations
- 2 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. Fiber supplements, particularly psyllium, can bind levothyroxine in the gastrointestinal tract and reduce its absorption. Studies have shown that concurrent fiber intake can decrease levothyroxine bioavailability, potentially leading to subtherapeutic thyroid hormone levels.
Mechanism. Psyllium and other soluble fibers form a viscous gel matrix in the GI tract that can physically trap levothyroxine, reducing its contact with the absorptive intestinal surface. The fiber-drug complex may be excreted before absorption occurs.
Recommendation. Separate levothyroxine and fiber supplements by at least 4 hours. Take levothyroxine in the morning on an empty stomach, and fiber supplements with later meals or at bedtime.
Minimum separation. 240
Sources (2)
- Liel Y et al. Evidence for a clinically important adverse effect of fiber-enriched diet on the bioavailability of levothyroxine in adult hypothyroid patients. J Clin Endocrinol Metab. 1996;81(2):857-859. PMID 8636317
- Ross DS. Treating hypothyroidism is not always easy: When to treat subclinical hypothyroidism, TSH goals in the elderly, and alternatives to levothyroxine monotherapy. Journal of Internal Medicine. 2022. PMID 34766382
Stack Score
How this pair moves the number.
Effect on the composite score
If both Levothyroxine and Psyllium Husk 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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