Do not use Isoniazid if:

• you are allergic to any ingredient in Isoniazid or have had severe side effects from Isoniazid, such as drug fever, chills, or arthritis;
• you have severe liver damage, active liver disease, or liver disease from previous use of Isoniazid.

• Check with your doctor before drinking alcohol while taking Isoniazid. Alcohol may increase the risk of liver problems.
• Eating foods high in tyramine (e.g., aged cheeses, red wines, beer, certain meats and sausages, liver, sour cream, soy sauce, raisins, bananas, avocados) while you use Isoniazid may cause severe high blood pressure. Do not eat foods high in tyramine while you take Isoniazid. Ask your health care provider for a complete list of foods you should avoid. Seek medical attention at once if symptoms of severe high blood pressure occur. These may include severe headache, fast or irregular heartbeat, sore or stiff neck, nausea, vomiting, sweating, enlarged pupils, or sensitivity to light.
• Isoniazid only works against TB bacteria; it does not treat viral infections (e.g., the common cold).
• Be sure to use Isoniazid for the full course of treatment. If you do not, the medicine may not clear up your infection completely. The bacteria could also become less sensitive to this or other medicines. This could make the infection harder to treat in the future.
• Contact your doctor right away if stomach pain or cramps, severe diarrhea, or bloody stools occur. Do not treat diarrhea without first checking with your doctor.
• Diabetes patients - Isoniazid may affect your blood sugar. Check blood sugar levels closely. Ask your doctor before you change the dose of your diabetes medicine.
• Lab tests, including liver function, may be performed while you use Isoniazid. These tests may be used to monitor your condition or check for side effects. Be sure to keep all doctor and lab appointments.
• Pregnancy and breast-feeding: If you become pregnant, contact your doctor. You will need to discuss the benefits and risks of using Isoniazid while you are pregnant. If you are or will be breast-feeding while you use Isoniazid, check with your doctor. Discuss any possible risks to your baby.

Check with your doctor if any of these most common side effects persist or become bothersome:

• Mild stomach upset.

• Severe allergic reactions (rash; hives; itching; difficulty breathing; tightness in the chest; swelling of the mouth, face, lips, or tongue); bloody stools; changes in vision; chills or fever; dark urine; general feeling of discomfort; joint pain or swelling; loss of appetite; memory problems; mental or mood changes; nausea; seizures; severe diarrhea; stomach pain; tingling or numbness in the hands or feet; unusual bruising or bleeding; unusual tiredness or weakness; vomiting; yellowing of the skin or eyes.

If you have any questions about Isoniazid, please talk with your doctor, pharmacist, or other health care provider.
Isoniazid is to be used only by the patient for whom it is prescribed. Do not share it with other people.