Propranolol and Methimazole: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Methimazole
Propranolol
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
Altered metabolism of the beta-adrenergic blocker
Interaction Deep Dive
Hyperthyroidism may increase the systemic clearance of beta blockers with a high extraction ratio. Once the patient becomes euthyroid, a dose reduction of the beta blocker may be necessary1.
Why it happens (mechanism)
Change from thyroid to euthyroid state may alter beta-adrenergic blocker clearance
Common questions
Can I take Propranolol and Methimazole together?
Altered metabolism of the beta-adrenergic blocker Always confirm with your pharmacist or prescriber before making any change.
How serious is the Propranolol and Methimazole interaction?
It is rated moderate. Can be significant — usually manageable with monitoring.
How quickly could this interaction happen?
The documented onset is "delayed". Effects tend to build up gradually over days to weeks.
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 Propranolol or Methimazole 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 anything you'd monitor while I'm on both?
References (1)
- Product Information: methimazole oral tablets, methimazole oral tablets. Caraco Pharmaceutical Laboratories, Ltd, Detroit, MI, 2008. DailyMed
Keep reading about Methimazole
Keep reading about Propranolol
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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