• Basic Info
• Top Questions
• Interactions

What should I avoid while taking isoniazid?

Avoid alcohol while taking isoniazid. Alcohol will increase the risk of damage to the liver during treatment with this medication.

Use caution with the foods listed below. They can interact with isoniazid and cause a reaction that includes a severe headache, large pupils, neck stiffness, nausea, vomiting, diarrhea, flushing, sweating, itching, irregular heartbeats, and chest pain. A reaction will not necessarily occur, but eat these foods with caution until you know if you will react to them. Call your doctor immediately if you experience any of these symptoms.

Eat the following foods with caution:

• cheeses, including American, Blue, Boursault, Brick, Brie, Camembert, Cheddar, Emmenthaler, Gruyere, Mozzarella, Parmesan, Romano, Roquefort, Stilton, and Swiss;

• sour cream and yogurt;

• beef or chicken liver, fish, meats prepared with tenderizer, bologna, pepperoni, salami, summer sausage, game meat, meat extracts, caviar, dried fish, herring, shrimp paste, and tuna;

• avocados, bananas, figs, raisins, and sauerkraut;

• soy sauce, miso soup, bean curd, and fava beans;

• yeast extracts;

• ginseng;

• chocolate;

• caffeine (coffee, tea, cola, etc.); and

• beer (alcoholic and nonalcoholic), red wine (especially Chianti), sherry, vermouth, and other distilled spirits.

What are the possible side effects of isoniazid?

If you experience any of the following serious side effects, stop taking isoniazid and seek emergency medical attention or contact your doctor immediately:

• an allergic reaction (difficulty breathing; closing of the throat; swelling of the lips, tongue, or face; or hives);

• unusual weakness or fatigue;

• nausea, vomiting, or loss of appetite;

• abdominal pain;

• yellow skin or eyes;

• dark urine;

• numbness or tingling in your hands or feet;

• seizures;

• blurred vision; or

• confusion or abnormal behavior.

Side effects other than those listed here may also occur. Talk to your doctor about any side effect that seems unusual or that is especially bothersome.

What other drugs will affect isoniazid?

Before taking isoniazid, tell your doctor if you are taking any of the following drugs:

• antacids. Aluminum salts will decrease the action of isoniazid. Do not take antacids that contain aluminum for 1 to 2 full hours before or after taking a dose of isoniazid.

• ketoconazole (Nizoral) and itraconazole (Sporanox). Isoniazid may decrease the actions of these antifungal medicines. Therefore, a fungal infection may not be adequately treated.

• rifampin (Rimactane, Rifadin) or rifabutin (Mycobutin).

• disulfiram (Antabuse). Unusual behavior and coordination difficulties may occur if these medicines are taken together.

Isoniazid may increase the effects of the following medicines:

• warfarin (Coumadin);

• carbamazepine (Tegretol);

• cycloserine (Seromycin);

• phenytoin (Dilantin), ethotoin (Peganone), and mephenytoin (Mesantoin);

• meperidine (Demerol);

• benzodiazepines such as alprazolam (Xanax), diazepam (Valium), lorazepam (Ativan), and temazepam (Restoril);

• theophylline (Theo-Dur, Theochron, Theolair, Elixophyllin, Slo-Phyllin, others);

• ethionamide (Trecator-SC).

You may require a dosage adjustment or special monitoring if you are taking any of the medicines listed above.

Drugs other than those listed here may also interact with isoniazid. Talk to your doctor and pharmacist before taking any prescription or over-the-counter medicines, including vitamins, minerals, and herbal products.

Where can I get more information?

Your pharmacist has additional information about isoniazid written for health professionals that you may read.

What does my medication look like?

Isoniazid is available with a prescription in tablet, syrup, and injection formulations. Ask your pharmacist any questions you have about this medication, especially if it is new to you.

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use this medication only for the indication prescribed.