The short answer
Not known in people. In rabbits given a crude water extract of garlic for two weeks, isoniazid reached less than half its usual total level in the blood, and its peak fell by about two thirds. Rifampicin, tested in other rabbits in the same study, did not change.
We found no study of garlic with isoniazid in people, and none on whether TB treatment works less well. Isoniazid is often given inside a combined TB tablet, so check the pack if you are not sure. If you are on TB treatment, tell your doctor before you start garlic supplements or extracts.
Isoniazid is sold in India as Isonex, and it is often part of combined TB tablets.
At a glance
| What was seen | How it may work | Direction | Evidence |
|---|---|---|---|
| Isoniazid peak and total exposure less than half after two weeks of garlic extract (rabbits)[1] | Less absorbed from the gut; elimination unchanged | Less isoniazid in the blood | Animal |
No listing is not a clearance. A missing interaction here never means a combination is safe.
The evidence, study by study
Rabbit study, 2006 Animal
Sixteen rabbits were given a single dose of isoniazid or rifampicin, eight per drug, then two weeks of a crude water extract of garlic by mouth, then the same drug again. Isoniazid's peak level fell from 15.4 to 5.4 micrograms per mL and its total exposure (AUC) from 76.7 to 34.3. It was cleared at the same rate, which points to less being absorbed. Rifampicin did not change, and rabbit results cannot tell us whether TB treatment works less well in people.[1]
What your doctor may watch for
- How your TB treatment is going, at the follow-up visits and tests your doctor arranges.
- Liver tests, if your doctor is monitoring them during TB treatment.
What to tell your prescribing doctor
You can read this out, or show them this page:
“I am on TB treatment (names of tablets), and I am taking, or planning to take, garlic (capsules, extract or raw cloves, and how much). In rabbits, garlic extract lowered isoniazid levels by more than half. Is this a concern for my treatment?”
Withheld until review
Questions people ask
Is garlic in food a problem with TB medicines?
The rabbit study used a crude water extract of garlic, not cooked garlic. Nobody has measured the effect of garlic in everyday food on isoniazid in people.[1]
Would taking garlic at a different time from my TB tablets help?
No study has tested a time gap between garlic and isoniazid, so we cannot say that one helps. Ask your TB doctor.[1]
Related
Pippali, black pepper and rifampicin (TB medicine)
Piperine, the compound in pippali and black pepper, is added to one Indian TB capsule to boost rifampicin. Adding it yourself is untested.
InteractionGarlic and HIV medicines (protease inhibitors)
Two people on darunavir had too little drug in the blood and their viral load rebounded after eating garlic. Garlic caplets halved saquinavir levels.
InteractionGarlic and blood thinners (warfarin, aspirin, clopidogrel)
Health agencies warn garlic supplements may raise bleeding risk. Two small studies on warfarin found no effect, but they cannot rule out rarer bleeding.
Sources
Updated 4 November 2026
Taking garlic with other medicines? A vaidya can check your full list.
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