Drug interactions
Isoniazid + Levonorgestrel oral / ethinylestradiol / ferrous bisglycinate
Severity: Minor
Isoniazid and Levonorgestrel oral / ethinylestradiol / ferrous bisglycinate: 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
Isoniazid is a weak CYP3A4 inhibitor in some settings and could modestly raise hormone exposure, but this is of little clinical relevance. The real concern in tuberculosis treatment is the rifamycins, not isoniazid, which reduce contraceptive efficacy. Isoniazid alone has not been shown to compromise contraception.
What this interaction means in plain words
Isoniazid and Levonorgestrel oral / ethinylestradiol / ferrous bisglycinate have a small, usually unimportant interaction. Most people can take both; the pharmacist may still mention it so that any unexpected effect is recognised.
Why it happens
Possible weak CYP3A4 inhibition by isoniazid, which could slightly raise ethinylestradiol and levonorgestrel concentrations.
What to do
No change is usually needed for isoniazid alone. If rifampicin or rifabutin is added, advise a non-hormonal or additional contraceptive method.
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 Isoniazid
Frequently asked questions
Can I take Isoniazid with Levonorgestrel oral / ethinylestradiol / ferrous bisglycinate?
MediHelp rates the interaction as minor. Isoniazid and Levonorgestrel oral / ethinylestradiol / ferrous bisglycinate have a small, usually unimportant interaction. Most people can take both; the pharmacist may still mention it so that any unexpected effect is recognised. Isoniazid is a weak CYP3A4 inhibitor in some settings and could modestly raise hormone exposure, but this is of little clinical relevance. The real concern in tuberculosis treatment is the rifamycins, not isoniazid, which reduce contraceptive efficacy. Isoniazid alone has not been shown to compromise contraception.
How serious is the interaction between Isoniazid and Levonorgestrel oral / ethinylestradiol / ferrous bisglycinate?
MediHelp rates it minor, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: No change is usually needed for isoniazid alone. If rifampicin or rifabutin is added, advise a non-hormonal or additional contraceptive method.
What other medicines interact with Isoniazid?
MediHelp also lists interactions of Isoniazid with, for example, Bacillus calmette-guerin substrain tice, Benzhydrocodone / acetaminophen, Carbamazepine. The full list is on the Isoniazid page.
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