• Basic Info
• Top Questions
• Interactions

What happens if I miss a dose?

Take the missed dose as soon as you remember. If it is almost time for the next regularly scheduled dose, skip the missed dose and take the next one as directed. Do not take a double dose of this medication.

What happens if I overdose?

Seek emergency medical attention if an overdose is suspected.

Symptoms of an isoniazid overdose include nausea, vomiting, dizziness, slurring of speech, blurred vision, visual hallucinations, seizures, coma, and death.

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.