Drug interactions
Levonorgestrel oral / ethinylestradiol / ferrous bisglycinate + Levothyroxine
Severity: Moderate
Levonorgestrel oral / ethinylestradiol / ferrous bisglycinate and Levothyroxine: 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
Estrogen in combined contraceptives raises thyroxine-binding globulin, increasing total thyroxine binding and lowering free hormone. Patients on levothyroxine replacement may become relatively hypothyroid and need a higher dose. The iron component may also reduce levothyroxine absorption if taken together.
What this interaction means in plain words
Levonorgestrel oral / ethinylestradiol / ferrous bisglycinate and Levothyroxine 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
Estrogen-induced increase in thyroxine-binding globulin reduces free thyroid hormone; iron may additionally chelate levothyroxine in the gut.
What to do
Check TSH about 6 to 12 weeks after starting or stopping the contraceptive and adjust levothyroxine dose accordingly. Separate levothyroxine from any iron-containing tablets by at least 4 hours.
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 Levothyroxine
Frequently asked questions
Can I take Levonorgestrel oral / ethinylestradiol / ferrous bisglycinate with Levothyroxine?
MediHelp rates the interaction as moderate. Levonorgestrel oral / ethinylestradiol / ferrous bisglycinate and Levothyroxine 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. Estrogen in combined contraceptives raises thyroxine-binding globulin, increasing total thyroxine binding and lowering free hormone. Patients on levothyroxine replacement may become relatively hypothyroid and need a higher dose. The iron component may also reduce levothyroxine absorption if taken together.
How serious is the interaction between Levonorgestrel oral / ethinylestradiol / ferrous bisglycinate and Levothyroxine?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Check TSH about 6 to 12 weeks after starting or stopping the contraceptive and adjust levothyroxine dose accordingly. Separate levothyroxine from any iron-containing tablets by at least 4 hours.
What other medicines interact with Levothyroxine?
MediHelp also lists interactions of Levothyroxine with, for example, Cholestyramine, Sodium iodide i-131, Tiratricol. The full list is on the Levothyroxine page.
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