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Updated September 07, 2015.

Isoniazid is a Tuberculosis drug. You may take it when you're not sick, but only have a bit of TB - latent TB. You may also take this same medication if you are sick with active TB.

How is it taken?

For those taking the drug for TB prophylaxis, it is usually taken once a day for 9 months (in some cases 6 months). 

Others take INH as part of a combination regimen with other medications to treat active TB.


It's  important that the medication is taken as directed with the other medications prescribed.

You should take the pill at the same time every day. You may wish to use a pillbox, a text message reminder, a note on a food cabinet or near your keys to remember. You may even have someone give you the med daily as part of DOTS (Daily Observed Therapy Short Course).

If you forget a pill but remember a few hours later, you can take it. If you forget the pill for days, do not try to double up and take multiple pills on the same day. Extra doses can be dangerous.

Is this the same as INH?

Yes, Isoniazid is also called INH for short after the drug name isonicotinylhydrazine.

Why was I given vitamins with INH?

B6 vitamins are given with Isoniazid to reduce the chance of an underlying B6 deficiency. Such a deficiency with INH use can be tied to developing side effects, like a peripheral neuropathy - tingling and loss of sensation (nerve damage) in hands and feet.

What are other side effects?

Isoniazid can lead to severe - and even fatal - liver problems.

It is important to follow up on any lab appointments or visits with yout healthcare provider. You should tell your clinic or doctor immediately if you have: yellow eyes, yellow skin, lack of energy, tiredness, loss of appetite, dark urine, light (or clay colored) stools, vomiting - while on Isoniazid.

Please tell your doctor about any alcohol or drug use as this can affect your risk for liver problems.

Any other side effects?

Isoniazid can cause tingling in hands or feet, due to nerve damage. Others may have vision problems. Some can have a reaction that can cause a rash, which can be serious. Some may even develop drug-induced lupus. Others may have psychosis or seizures (especially with an overdose).

Others may have reactions with fever, swollen glands. Some may have blood abnormalities.

It's important to talk your healthcare provider about whether you are pregnant or may become pregnant while taking this medication.

These symptoms - and any other worrisome symptoms - should be discussed with your healthcare provider or should prompt an urgent medical examination.

Can I take Isoniazid with other drugs?

If you're taking isoniazid for active Tuberculosis, you need to take other drugs. It cannot be taken alone for treatment for active TB.

It's important to tell your doctor about any other drugs you are taking. This particularly includes drugs that can affect your liver - Tylenol (Acetaminophen, Paracetamol), drugs for seizures or mood disorders - carbamazepine (Tegretol), phenytoin (Dilantin), valproic acid (VPA, Depakene, Depakote), as well as ketoconazole (Nizoral), theophylline (Theobid, Theo-Dur)

You should also discuss with your healthcare provider if you are taking any herbal or natural medications. Some of these can affect your liver.

How do you know you have a "little bit of TB"?

Well, you may have had a known exposure to TB, especially if you are at high risk (have HIV, are very young or old, take immunosuppressive drugs). You may have had a PPD test that showed past exposure or an interferon test. There may be other reasons why your healthcare provider was concerned that you have some TB inside of you.

This does not mean you are sick. This little bit of TB may be "latent". This means it causes no problems for you. Instead, it could in the future wake up and cause active Tuberculosis.

What is Tuberculosis?

Tuberculosis - also called TB for short or consumption in the old days - is a disease that is inside about 1 in 3 people worldwide. That is to say, many people have latent TB. Many of them do not have access to drugs that prevent it from becoming an active infection.

Many do go on to develop active infection. About 9 million people become sick each year; 1.5 million die worldwide. In the US, a little under 10,000 became sick with TB in 2013.

Illness usually involves the lungs, with fever, weight loss, night sweats, and generalized fatigue common. Some cough blood; some develop holes in their lungs. Others have infections of their spine or joints; some have meningitis or intestinal infections.

Can I drink alcohol with INH?

It's important to talk with your doctor about your alcohol intake. Alcohol can cause problems while on INH as it could increase liver damage. You should discuss any alcohol use with your doctor. If you already have liver damage from alcohol or stopping drinking will be a problem, this is important to discuss with your healthcare provider.

Is INH the only drug I can take for latent TB?

Some may prescribe a 12-Dose (Isoniazid and Rifapentine) once weekly drug course. Others may prescribe 4 months of rifampin. Others may need a different drug if they have been exposed to drug resistant TB.

What does INH do?

The drug acts to inhibit lipid and DNA synthesis stopping the building of cell walls in the mycobacteria that cause Tuberculosis. 

What if I take too much?

If you, or someone else, takes too much call your local poison control center 1-800-222-1222. If serious, call 911.

B6 vitamins can be used as part of the treatment of an overdose. So you may want to take these along, if handy, while seeking medical care to ensure they are available.

Keep pill bottles away from children. This drug can be dangerous if overdosed.