Drug interactions
Lycopus + Methimazole
Severity: Moderate
Lycopus and Methimazole: moderate 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
Lycopus (gypsywort) extracts have antithyrotropic activity and may reduce thyroid hormone activity, including peripheral T4 to T3 conversion. Combined with methimazole this could add to the antithyroid effect and raise the risk of over-suppression and hypothyroidism.
What this interaction means in plain words
Lycopus and Methimazole can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken.
Why it happens
Additive antithyroid pharmacodynamic effects, with lycopus inhibiting TSH binding and peripheral T4 to T3 conversion.
What to do
Avoid starting lycopus in patients on methimazole where possible. If it is used, monitor TSH and free T4/T3 every 4-6 weeks and reduce the methimazole dose if hypothyroidism appears.
What to ask your pharmacist
- Should I take them at different times of day?
- Does the dose of either medicine need to change?
- Is there anything I should avoid, such as alcohol or certain foods, while on both?
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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 Lycopus with Methimazole?
MediHelp rates the interaction as moderate. Lycopus and Methimazole can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken. Lycopus (gypsywort) extracts have antithyrotropic activity and may reduce thyroid hormone activity, including peripheral T4 to T3 conversion. Combined with methimazole this could add to the antithyroid effect and raise the risk of over-suppression and hypothyroidism.
How serious is the interaction between Lycopus and Methimazole?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Avoid starting lycopus in patients on methimazole where possible. If it is used, monitor TSH and free T4/T3 every 4-6 weeks and reduce the methimazole dose if hypothyroidism appears.
What other medicines interact with Methimazole?
MediHelp also lists interactions of Methimazole with, for example, Carbamazepine, Clozapine, Propylthiouracil. The full list is on the Methimazole page.
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