From €18.04 per pack.
Source: Official public price (French medicines database), 8 Nov 2026. What you pay at the counter can be higher (pharmacy fees, insurance).
Prices in other countries are not what you will pay where you live; they show how prices compare.
In France, Isoniazid costs from €18.04 per pack (Official public price (French medicines database)).
Ask the pharmacist for a generic version with the same active ingredient and strength: it works the same and usually costs much less. Compare a few licensed pharmacies, and never buy medicine from unlicensed sellers to save money.
Check the registration number on the pack with PillVera, look at the expiry date, and buy from a licensed or verified pharmacy. A price far below everyone else's is a warning sign.