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Isoniazid oral

Important Note

The following information is intended to supplement, not substitute for, the expertise and judgment of your physician, pharmacist or other healthcare professional. It should not be construed to indicate that use of the drug is safe, appropriate, or effective for you. Consult your healthcare professional before using this drug.




WARNING: Rarely, this medication has caused severe (sometimes fatal) liver problems (e.g., hepatitis). Liver problems increase with age and with daily use of alcohol. Hepatitis can develop with use of this drug at any time during treatment. Stop using this medication and notify your doctor immediately if you develop unusual fatigue, weakness, loss of appetite, nausea, vomiting, dark urine, yellowing of the eyes or skin, or stomach or abdominal pain. Your doctor may decide to slowly restart isoniazid after these symptoms disappear and lab tests return to normal. People with active (acute) liver problems should not use this medication for preventative treatment until after the liver problems have stopped. Your doctor will monitor your liver function tests at least every month to discuss your progress.


This medication is used to prevent and treat tuberculosis.

How To Use

This medication is best taken on an empty stomach 1 hour before or 2 hours after meals. But it may be taken with food or milk if stomach upset occurs. Take as directed. Do not stop taking this medication without your doctor's approval. Stopping therapy early may result in ineffective treatment and the infection could recur. Vitamin B6 (pyridoxine) supplements may be prescribed in addition to this medication to prevent numbness and tingling.

Side Effects

May cause stomach upset, heartburn, nausea or dizziness. These effects should disappear as your body adjusts to the medication. If these effects persist or become bothersome, inform your doctor. Notify your doctor if you experience: blurred vision, darkening of the urine, skin rash, yellowing of the eyes or skin, numbness or tingling of the hands or feet. In the unlikely event you have an allergic reaction to this drug, seek immediate medical attention. Symptoms of an allergic reaction include: rash, itching, swelling, dizziness, trouble breathing. If you notice other effects not listed above, contact your doctor or pharmacist.


Tell your doctor your medical history, especially of: kidney or liver problems, diabetes, alcohol use, previous treatment for tuberculosis, any allergies. Alcohol can reduce the effectiveness of isoniazid and increase side effects. Minimize alcohol consumption. This medication should be used only when clearly needed during pregnancy. Discuss the risks and benefits with your doctor. Isoniazid is excreted into breast milk. Consult your doctor before breast-feeding.

Drug Interactions

Tell your doctor of all medications you may use (both prescription and nonprescription) especially of: other MAO inhibitors (e.g., furazolidone, linezolid, moclobemide, phenelzine procarbazine, selegiline, isocarboxazid, tranylcypromine)., adrenaline-like drugs (e.g., sympathomimetics such as ephedra, pseudoephedrine, phenylpropanolamine), serotonin-type drugs (including SSRI antidepressants and triptans such as sumatriptan), aluminum-containing antacids, disulfiram, phenytoin, rifampin, carbamazepine. It is very important that you follow special dietary restrictions in order to limit the amount of tyramine in your diet while you are taking this medicine. Foods and beverages high in tyramine should be avoided (see list below). Excessive amounts of coffee, chocolate, sour cream, or avocados have also produced symptoms of high blood pressure in some cases. High tyramine content foods include: aged cheeses (cheddar, camembert, emmenthaler, brie, stilton blue, gruyere, gouda, brick, bleu, roquefort, boursault, parmesan, romano, provolone, liederdranz, colby, edam), aged/dried/fermented/salted/smoked/pickled/processed meats and fish (includes bacon, summer sausage, liverwurst, hot dogs, corned beef, pepperoni, salami, bologna, ham, mortadella, pickled or dried herring), banana peel, beef and chicken liver (stored, not fresh), bouillon cubes, commercial gravies, concentrated yeast extracts (marmite), fava beans, Italian green beans, broad beans, fermented bean curd, homemade yeast-leavened bread, kim chee (Korean fermented cabbage), miso, orange pulp, overripe or spoiled fruits, packaged soups, red wine, sauerkraut, sherry, snow pea pods, sourdough bread, soy sauce, soya bean, soya bean paste, tap beer and ale, vermouth. Moderate-to-low tyramine content foods include: alcohol-free beer, avocados, bananas, bottled beer and ale, chocolate and products made with chocolate, coffee, cola, cultured dairy products (e.g. buttermilk, yogurt, sour cream), distilled spirits, eggplant, canned figs, fish roe (caviar), green bean pods, pate, peanuts, port wine, raisins, raspberries, red plums, spinach, tomatoes, white wine. Tell your doctor or pharmacist immediately if you notice symptoms of high blood pressure such as fast or slow heartbeat, vomiting, sweating or headache, chest pain, sudden vision changes, one-sided weakness or slurred speech. Contact your healthcare professional (e.g., doctor, pharmacist or dietician) for more information, including recommendations for your diet. This drug may interfere with the effectiveness of birth control pills. Discuss using other methods of birth control with your doctor. Isoniazid can cause false positive results in diabetics using Clinitest to test their urine. Consult your doctor or pharmacist for recommendations. Do not start or stop any medicine without doctor or pharmacist approval.


If overdose is suspected, contact your local poison control center or emergency room immediately. Symptoms of overdose may include nausea; vomiting; dizziness; slurring of speech; blurred vision; numbness, tingling, or burning of your arms, hands, legs, or feet; joint pain; hallucinations; and loss of consciousness.


Periodic eye tests may be done while you are taking this medication.

Missed Dose

If you miss a dose, take as soon as remembered; do not take if it is almost time for the next dose, instead, skip the missed dose and resume your usual dosing schedule. Do not "double-up" the dose to catch up.


Store at room temperature away from moisture and sunlight. Do not store in the bathroom. Do not freeze liquid forms of this medicine.