Orlistat and Levothyroxine: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 9, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Orlistat
Levothyroxine
How we grade severity & evidence
Severity levels
- Contraindicated: These should generally not be used together.
- Major: Potentially serious — often needs a change or close monitoring.
- Moderate: Can be significant — usually manageable with monitoring.
- Minor: Usually limited clinical impact.
Evidence grades
- Established: Well documented — supported by controlled studies or strong clinical data.
- Probable: Good supporting evidence, though not definitively proven.
- Suspected: Some evidence suggests this interaction, but it is not well established.
- Possible: Limited or conflicting evidence; the interaction may occur.
- Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.
Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.
What happens
Reduced efficacy of levothyroxine and an increased risk of hypothyroidism
Interaction Deep Dive
Concomitant use of levothyroxine and orlistat may reduce levothyroxine efficacy by binding to and delaying or preventing levothyroxine absorption, potentially resulting in hypothyroidism. If concurrent use of levothyroxine and orlistat is required, patient should be monitored for changes in thyroid function23. Administer levothyroxine and orlistat at least 4 hours apart 1.
Why it happens (mechanism)
Reduced absorption of levothyroxine by binding levothyroxine with orlistat
Literature reports
1 report — tap to read
a) Hypothyroidism has been reported in patients treated concomitantly with orlistat and levothyroxine postmarketing 1.
Common questions
Can I take Orlistat and Levothyroxine together?
Reduced efficacy of levothyroxine and an increased risk of hypothyroidism Always confirm with your pharmacist or prescriber before making any change.
How serious is the Orlistat and Levothyroxine interaction?
It is rated major. Potentially serious — often needs a change or close monitoring.
How quickly could this interaction happen?
The documented onset is "unspecified". The timing of this interaction is not well characterized.
How strong is the evidence for this interaction?
The evidence is graded "theoretical". Predicted from the drugs' pharmacology; not yet confirmed in people.
From our Q&A
Real reader questions about these medications, each personally answered by our pharmacist:
Questions for your pharmacist
- Does my dose of Orlistat or Levothyroxine need adjusting while I take them together?
- What symptoms should prompt me to call you or my prescriber right away?
- Does the timing of my doses matter for this combination?
- Is there a safer alternative to one of these medications for me?
References (3)
- Product Information: XENICAL oral capsules, orlistat oral capsules. H2-Pharma, LLC (per Dailymed), Montgomery, AL, 2023. DailyMed
- Product Information: SYNTHROID(R) oral tablets, levothyroxine sodium oral tablets. AbbVie Inc (per FDA), North Chicago, IL, 2024. DailyMed
- Product Information: TIROSINT(R)-SOL oral solution, levothyroxine sodium oral solution. IBSA Pharma Inc. (per FDA), Parsippany, NJ, 2023. DailyMed
Keep reading about Orlistat
Keep reading about Levothyroxine
These medications also interact with supplements
Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:
major · moderate · minor — check everything you take with our drug–supplement interaction checker.
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