Isoniazid: what it does and what to watch
Also known as: Anti-tuberculosis medicine, INH · Antibiotic used specifically against tuberculosis · Updated 2026-08-20 · Educational — not medical advice
In plain language: This medicine interferes with the building of mycolic acids, a waxy component unique to the cell wall of the tuberculosis bacterium. Without an intact cell wall, actively dividing bacteria weaken and die. Because tuberculosis bacteria can hide in a slow-growing or dormant state, this medicine is usually combined with others to attack the bacteria from multiple angles.
What it's used for
- Treatment of active tuberculosis as part of combination therapy
- Preventive treatment for latent tuberculosis infection
Common side effects
- Nausea
- Stomach upset
- Mild tingling in the hands or feet
- Fatigue
- Loss of appetite
Get medical help if…
Liver inflammation, which can range from mild enzyme elevation to more serious liver injury
Peripheral nerve damage causing numbness, tingling, or burning in the hands and feet, particularly without vitamin B6 supplementation
Rare psychiatric changes, memory difficulty, or seizures at higher exposure
Lab values it can move
Few guides tell you this part: medicines show up in blood work. If you take Isoniazid and a value below looks off on your report, this may be part of the story — never stop a medicine without your doctor.
Liver enzymes are checked before starting and periodically during treatment, since liver inflammation is a recognized effect of this medicine.
SGPT (ALT)This enzyme is monitored alongside ALT to track liver health throughout the treatment course.
SGOT (AST)Good to know
- Vitamin B6 (pyridoxine) is commonly co-prescribed alongside this medicine to help prevent nerve damage, a well-established practice
- Liver function is monitored, particularly in people who drink alcohol or take other liver-affecting medicines
- Report tingling, numbness, or burning in the hands or feet promptly
- Complete the full course exactly as prescribed even after feeling better, since tuberculosis bacteria can survive incomplete treatment
- Avoid or limit alcohol during treatment to reduce strain on the liver
Questions people ask
Why am I also given vitamin B6 with this medicine?
This medicine can interfere with how the body uses vitamin B6, and low B6 levels contribute to the nerve damage some people develop during treatment, felt as tingling or burning in the hands and feet. Co-prescribing vitamin B6 alongside this medicine is a standard, well-established practice that helps prevent this nerve-related side effect from developing.
What symptoms of nerve damage should I watch for?
Tingling, numbness, burning, or a pins-and-needles sensation, usually starting in the feet and sometimes moving to the hands, are the main early signs of nerve damage from this medicine. Reporting these symptoms promptly allows a prescriber to check B6 levels and adjust supplementation before the nerve changes become more pronounced or lasting.
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