Get emergency medical help if you have signs of an allergic reaction (hives, rash, feeling light-headed, wheezing, difficult breathing, swelling in your face or throat) or a severe skin reaction (fever, sore throat, burning in your eyes, skin pain, red or purple skin rash that spreads and causes blistering and peeling).
Seek medical treatment if you have a serious drug reaction that can affect many parts of your body. Symptoms may include: skin rash, fever, swollen glands, muscle aches, severe weakness, unusual bruising, or yellowing of your skin or eyes.
Call your doctor at once if you have:
severe stomach pain, diarrhea that is watery or bloody;
chest pain, cough, shortness of breath;
a light-headed feeling, like you might pass out;
easy bruising, unusual bleeding (nosebleeds, bleeding gums);
pounding heartbeats or fluttering in your chest;
flu symptoms--fever, chills, body aches, headache, weakness, nausea, vomiting; or
liver problems--upper stomach pain, tiredness, loss of appetite, dark urine, clay-colored stools, jaundice (yellowing of the skin or eyes).
Common side effects may include:
red discoloration of your teeth, sweat, urine, saliva, and tears;
heartburn, gas, upset stomach, loss of appetite;
nausea, vomiting, diarrhea;
fever;
headache, dizziness, drowsiness, tiredness;
muscle weakness, pain in your arms or legs;
problems with balance or muscle movement;
numbness; or
confusion, changes in behavior, trouble concentrating.
This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.
 Rifampin side effects (more detail)
