See also Warning section.

Before taking isoniazid, tell your doctor or pharmacist if you are allergic to it; or if you have any other allergies. This product may contain inactive ingredients, which can cause allergic reactions or other problems. Talk to your pharmacist for more details.

Before using this medication, tell your doctor or pharmacist your medical history, especially of: previous severe reaction from isoniazid (such as liver disease), liver disease, alcohol use, HIV infection, kidney disease, diabetes, numbness/tingling of arms/legs (peripheral neuropathy), recent childbirth.

Before having surgery, tell your doctor or dentist about all the products you use (including prescription drugs, nonprescription drugs, and herbal products).

Alcohol may increase the risk of liver disease. Avoid alcoholic beverages while using this medication.

This product may cause live bacterial vaccines (such as BCG vaccine) to not work well. Tell your health care professional that you are using this medication before having any immunizations/vaccinations.

Liquid forms of this medication may contain sugar. Caution is advised if you have diabetes or any other condition that requires you to limit/avoid sugar. Ask your doctor or pharmacist about using this product safely.

During pregnancy, this medication should be used only when clearly needed. Discuss the risks and benefits with your doctor.

This product passes into breast milk but is unlikely to harm a nursing infant. Consult your doctor before breastfeeding.