Drug interactions
Heparin + Methimazole
Severity: Minor
Heparin and Methimazole: minor interaction.
Last updated
For healthcare professionals — reference only. This page is a brief summary, not medical advice and not a substitute for official labeling or clinical judgement. Always verify before prescribing or dispensing.
Summary
Hyperthyroidism may increase sensitivity to anticoagulants, so treating it with methimazole may reduce anticoagulant response with warfarin. The effect on heparin is not established and likely small.
What this interaction means in plain words
Heparin and Methimazole have a small, usually unimportant interaction. Most people can take both; the pharmacist may still mention it so that any unexpected effect is recognised.
Heparin belongs to Cardiovascular; Methimazole belongs to Endocrine.
Why it happens
Changes in thyroid status alter clotting factor turnover, which matters mainly for vitamin K antagonists rather than heparin.
What to do
Monitor aPTT or anti-Xa as part of routine heparin therapy, especially as thyroid status changes.
What to ask your pharmacist
- Is there anything I should notice while taking both?
- Do I need to tell my doctor at the next visit?
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Other interactions of Heparin
- Defibrotide + Heparin Contraindicated
- Heparin + Ketorolac Contraindicated
- Heparin + Oritavancin Contraindicated
- Acemetacin + Heparin Major
- Acetylsalicylic acid + Heparin Major
- Alteplase + Heparin Major
Other interactions of Methimazole
- Carbamazepine + Methimazole Major
- Clozapine + Methimazole Major
- Methimazole + Propylthiouracil Major
- Methimazole + Sodium iodide i-131 Major
- Iodinated glycerol + Methimazole Moderate
- Iodine + Methimazole Moderate
Frequently asked questions
Can I take Heparin with Methimazole?
MediHelp rates the interaction as minor. Heparin and Methimazole have a small, usually unimportant interaction. Most people can take both; the pharmacist may still mention it so that any unexpected effect is recognised. Hyperthyroidism may increase sensitivity to anticoagulants, so treating it with methimazole may reduce anticoagulant response with warfarin. The effect on heparin is not established and likely small.
How serious is the interaction between Heparin and Methimazole?
MediHelp rates it minor, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Monitor aPTT or anti-Xa as part of routine heparin therapy, especially as thyroid status changes.
What other medicines interact with Heparin?
MediHelp also lists interactions of Heparin with, for example, Defibrotide, Ketorolac, Oritavancin. The full list is on the Heparin page.
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