Is Fiber (Psyllium / Glucomannan) Safe with Levothyroxine?
Free · No account · based on published sources including NIH ODS, FDA drug labels, and peer-reviewed literature
Take levothyroxine 30–60 minutes before consuming fiber supplements, high-fiber meals, or fiber-enriched drinks. Do not take psyllium husk or glucomannan at the same time as levothyroxine.
Why this interaction occurs
Soluble fiber supplements such as psyllium husk and glucomannan can bind levothyroxine in the GI tract, reducing its absorption and bioavailability. This is similar to the mechanism seen with cholestyramine (a bile acid sequestrant). Consistent high fiber intake may necessitate TSH monitoring and possible dose adjustment. The interaction is most relevant when fiber supplements are taken simultaneously with the morning levothyroxine dose.
Evidence
Evidence level: moderate.
Reported safety data
The FDA’s adverse event reporting system (FAERS) has received 302,514 reports mentioning Levothyroxine. This reflects reported cases involving the medication in general — not confirmed causation, and not specific to the Levothyroxine + supplement combination on this page.
FAERS reports are voluntary and cannot prove that a drug caused an event. Do not use report counts to assess the safety of this specific drug-supplement pair.
Frequently asked questions
Related interactions
All Fiber (Psyllium / Glucomannan) interactions → · All Levothyroxine interactions →
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Educational only — not medical advice.
Always confirm with your doctor or pharmacist.