SIDE EFFECTS: See also Warning section. Nausea/vomiting, upset stomach, heartburn, or headache may occur. If any of these effects persist or worsen, tell your doctor or pharmacist promptly. This medication may cause urine, sweat, saliva, or tears to change color (yellow, orange, red, or brown). This effect is harmless and will go away when the medication is stopped. However, teeth and contact lens staining may be permanent. Remember that your doctor has prescribed this medication because he or she has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects. Tell your doctor right away if any of these unlikely but serious side effects occur: numbness/tingling of arms/legs, painful/swollen joints. Tell your doctor right away if any of these rare but serious side effects occur: signs of kidney problems (such as change in the amount of urine, bloody urine), increased thirst/urination, vision changes, easy bruising/bleeding, mental/mood changes (such as confusion, psychosis), seizures. This medication may rarely cause a severe intestinal condition (Clostridium difficile-associated diarrhea) due to a type of resistant bacteria. This condition may occur during treatment or weeks to months after treatment has stopped. Do not use anti-diarrhea or opioid medications if you have any of the following symptoms because these products may make them worse. Tell your doctor right away if you develop: persistent diarrhea, abdominal or stomach pain/cramping, blood/mucus in your stool. A very serious allergic reaction to this drug is rare. However, get medical help right away if you notice any symptoms of a serious allergic reaction, including: fever that doesn't go away, new or worsening lymph node swelling, rash, itching/swelling (especially of the face/tongue/throat), severe dizziness, trouble breathing. This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist. In the US - Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088 or at www.fda.gov/medwatch. In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.

PRECAUTIONS: See also Warning section. Before taking this product, tell your doctor or pharmacist if you are allergic to rifampin or isoniazid; or to other rifamycins (such as rifabutin, rifapentine); 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, kidney disease, alcohol use, HIV infection, diabetes, numbness/tingling of arms/legs (peripheral neuropathy), recent childbirth, a certain blood disorder (porphyria). 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 typhoid vaccine) to not work as well. Do not have any immunizations/vaccinations while using this medication unless your doctor tells you to. During pregnancy, this product should be used only when clearly needed. When rifampin is taken during the last few weeks of pregnancy, the risk of bleeding in both mother and infant may be increased. Tell your doctor right away if you notice any bleeding in your newborn. 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 breast-feeding.

DRUG INTERACTIONS: See also How to Use section. Drug interactions may change how your medications work or increase your risk for serious side effects. This document does not contain all possible drug interactions. Keep a list of all the products you use (including prescription/nonprescription drugs and herbal products) and share it with your doctor and pharmacist. Do not start, stop, or change the dosage of any medicines without your doctor's approval. Some products that may interact with this drug include: acetaminophen, carbamazepine, disulfiram, MAO inhibitors (isocarboxazid, linezolid, methylene blue, moclobemide, phenelzine, procarbazine, rasagiline, safinamide, selegiline, tranylcypromine), SSRI antidepressants (such as fluoxetine, sertraline), valproic acid. Rifampin can speed up the removal of other medications from your body, which may affect how they work. Examples of affected drugs include digoxin, nimodipine, phenytoin, ranolazine, tacrolimus, theophylline, certain anti-infectives (e.g., chloramphenicol, clarithromycin, dapsone, doxycycline, linezolid, telithromycin, zidovudine, quinolones such as ciprofloxacin) azole antifungals (such as itraconazole, ketoconazole), "blood thinners" (such as warfarin), calcium channel blockers (such as diltiazem, verapamil), HIV NNRTIs (such as delavirdine, etravirine, nevirapine), HIV protease inhibitors (such as atazanavir, ritonavir, saquinavir), among others. This medication may decrease the effectiveness of hormonal birth control such as pills, patch, or ring. This could cause pregnancy. Discuss with your doctor or pharmacist if you should use additional reliable birth control methods while using this medication. Also tell your doctor if you have any new spotting or breakthrough bleeding, because these may be signs that your birth control is not working well. This medication may interfere with certain laboratory tests (including folate/vitamin B12 levels, urine glucose tests), possibly causing false test results. Make sure laboratory personnel and all your doctors know you use this drug.

OVERDOSE: If someone has overdosed and has serious symptoms such as passing out or trouble breathing, call 911. Otherwise, call a poison control center right away. US residents can call their local poison control center at 1-800-222-1222. Canada residents can call a provincial poison control center. Symptoms of overdose may include: severe stomach/abdominal pain, unusual tiredness/weakness, yellowing eyes/skin, vision changes, slow/shallow breathing, severe drowsiness.