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Overview: Isoniazid is used with other medicines to treat tuberculosis. It can also be used to prevent tuberculosis. Common side effects include nerve problems, nausea, vomiting, and an upset stomach. It is important to complete your prescribed course of isoniazid, even if your symptoms get better or go away. This will reduce the risk that future infections are resistant to isoniazid or other similar medicines.

Uses

What is isoniazid used for?

Isoniazid is commonly used to treat tuberculosis (along with other medicine). Isoniazid can also be used to prevent tuberculosis in people at high risk of infection. 

Isoniazid may not be the right drug for some of the infections listed above, depending on which germs are causing the infection. Bacteria in some locations may have developed resistance to isoniazid, which will make it not work as well.

Isoniazid may also be used for other conditions as determined by your health care provider.

How does isoniazid work (mechanism of action)?

Isoniazid helps stop the tuberculosis bacteria from multiplying in your body. This makes it easier for your body to fight off the infection and get rid of the bacteria.

How is isoniazid supplied (dosage forms)?

Brands and other names

  • Hyzyd
  • INH
  • Laniazid
  • Nydrazid

Dosage forms and strengths

  • 50 mg/5 mL oral solution
  • 100 mg oral tablets
  • 300 mg oral tablets

How should I store isoniazid?

Isoniazid should be stored at room temperature, between 68 F and 77 F (20 C and 25 C). It can be exposed to temperatures between 59 F and 86 F (15 C and 30 C) for shorter periods of time, such as when you’re  transporting it. Store it in a cool, dry place, and protect it from light and moisture. 

Side Effects

What are the most common side effects of isoniazid?

The most common side effects of isoniazid are listed below. Tell your health care provider if you have any of these side effects that bother you.

  • Nerve problems (see below)
  • Nausea
  • Vomiting
  • Upset stomach

There may be other side effects of isoniazid that are not listed here. Contact your health care provider if you think you are having a side effect of a medicine. In the U.S., you can report side effects to the FDA at www.fda.gov/medwatch or by calling 800-FDA-1088 (800-332-1088). In Canada, you can report side effects to Health Canada at www.health.gc.ca/medeffect or by calling 866-234-2345.

What are the serious side effects of isoniazid?

While less common, the most serious side effects of isoniazid are described below, along with what to do if they happen.

Liver Damage. Liver damage, also called hepatotoxicity, can happen when taking isoniazid. This can sometimes lead to death. Call your health care provider right away if you have any of the following symptoms of liver damage.

  • Nausea or vomiting
  • Stomach or belly pain
  • Fever
  • Weakness or unusual tiredness
  • Itching
  • Loss of appetite
  • Light-colored poop
  • Dark-colored urine (pee)
  • Your skin or the whites of your eyes turning yellowish in color (also called jaundice)

Nerve Problems. Nerves are the fibers that carry sensations from your body to the brain. Damage to these nerves, called peripheral neuropathy, can happen in people who are taking isoniazid. Stop taking isoniazid and call your health care provider if you have pain, burning, tingling, numbness, or weakness in your arms, hands, legs, or feet.

Severe Allergic Reactions. Isoniazid may cause allergic reactions, including a specific type of allergic reaction called DRESS. DRESS stands for drug reaction with eosinophilia and systemic symptoms. It is also sometimes called multi-organ hypersensitivity. This is a reaction that can affect many parts of the body, including your liver, kidneys, and heart. Stop taking the medicine and get help right away if you have any of the following symptoms of a serious allergic reaction.

  • Breathing problems or wheezing
  • Racing heart
  • Itching, skin rash, or pale red bumps on the skin called hives
  • Fever or general ill feeling
  • Swollen lymph nodes
  • Swelling of the face, lips, mouth, tongue, or throat
  • Shortness of breath, trouble swallowing, or throat tightness
  • Swelling in your feet, ankles, or legs
  • Nausea or vomiting
  • Dizziness, feeling lightheaded, or fainting
  • Stomach cramps
  • Joint pain
  • Dark-colored pee

Your skin or the whites of your eyes turning yellowish in color (also called jaundice)

Warnings & Precautions

Who should not use isoniazid?

Allergies to Ingredients. People who are allergic to any of the following should not take isoniazid.

  • Hyzyd
  • INH
  • Laniazid
  • Nydrazid
  • Isoniazid
  • Any of the ingredients in the specific product dispensed

Your pharmacist can tell you all of the ingredients in the specific isoniazid products they stock.

Previous Reaction to Isoniazid. People who have had a previous severe reaction to isoniazid, such as liver damage, joint pain, fever, or chills, should not take isoniazid.

Liver Disease. Isoniazid should not be used by those with active liver disease. 

What should I know about isoniazid before using it?

Do not take isoniazid unless it has been prescribed to you by a health care provider. Take it as prescribed.

Do not share isoniazid with other people, even if they have the same condition as you. It may harm them.

If you are taking the isoniazid liquid, use an accurate measuring device to measure your dose. A household spoon is not an accurate measuring device and may cause you to take the wrong dose. Ask your pharmacist to recommend a good measuring device.

Keep isoniazid out of the reach of children.

Your health care provider will likely do bloodwork before starting this medicine and while you are taking it to monitor the health of your liver. It is important to keep all appointments for bloodwork.

It is important to complete your prescribed course of isoniazid, even if your symptoms get better or go away. This will reduce the risk that future infections are resistant to isoniazid or other similar medicines.

What should I tell my health care provider before using isoniazid?

Tell your health care provider about all of your health conditions and any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. This will help them know if isoniazid is right for you.

In particular, make sure that you discuss any of the following.

Current and Past Health Conditions. Tell your health care provider if you have any of the following.

  • History of taking medicine to treat tuberculosis
  • Liver or kidney problems
  • Nerve problems
  • HIV or AIDS
  • Diabetes
  • Drinking alcohol often or in large amounts
  • Intravenous (IV) drug use

Other Medicines and Supplements. Isoniazid may interact with other medicines and supplements. Before taking isoniazid, tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using. See the Interactions section for more details.

Pregnancy. It is not known if or how isoniazid could affect pregnancy or harm an unborn baby. Tell your health care provider if you are pregnant or plan to become pregnant. Your health care provider will let you know if you should take isoniazid while you are pregnant or trying to get pregnant.

Breastfeeding. Isoniazid passes into breast milk. Tell your health care provider if you are breastfeeding or plan to breastfeed. Your health care provider will let you know if you should take isoniazid while breastfeeding.

Interactions

Does isoniazid interact with foods or drinks?

Do not take isoniazid with food. Taking isoniazid with food can make it not work as well. 

Avoid eating or drinking things with a lot of tyramine or histamine in them. These are things like cheese and red wine (high in tyramine) and certain fish like tuna (high in histamine). Isoniazid can interact with these foods, causing side effects like headaches, sweating, a fast heartbeat, flushing, and low blood pressure.

It is unknown if drinking alcohol will affect isoniazid. The risk of liver damage may be increased if you drink alcohol while taking isoniazid. It is best to avoid drinking alcohol while taking isoniazid.

Does isoniazid interact with other medicines (drug interactions)?

Always tell your health care provider about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements you are using.

In particular, make sure that you discuss if you are using any of the following before using isoniazid.

  • Acetaminophen, which is a medicine used for pain or fever
  • Carbamazepine (Carbatrol, Tegretol, and others), which is a medicine commonly used to treat seizures or nerve pain
  • Ketoconazole, which is a medicine used for fungal infections
  • Phenytoin (Dilantin, Phenytek, and others), which is a medicine to control seizures
  • Theophylline (Theo-24, Elixophyllin), which is a medicine for asthma or certain other breathing problems
  • Valproic acid, divalproex sodium, and valproate sodium (Depakote and others), which is a medicine used for seizures and other conditions

This may not be a complete list of medicines that can interact with isoniazid. Always check with your health care provider.

Does interact with other drugs you are taking?

Enter your medication into the WebMD interaction checker

Overdose/Missed Dose

What should I do if I accidentally use too much isoniazid?

If you or someone else has used too much isoniazid, get medical help right away, call 911, or contact a Poison Control center at 800-222-1222.

What should I do if I miss a dose of isoniazid?

If you miss a dose, take it as soon as you remember. If it is almost time for your next dose, skip the missed dose and only take the next dose. Do not take double or extra doses. 

It is important to complete your prescribed course of isoniazid, even if your symptoms get better or go away. This will reduce the risk that future infections are resistant to isoniazid or other similar medicines.