Rifampicin is mainly used to treat and prevent tuberculosis (TB). TB is an infection which mostly affects the lungs, but which can affect any part of your body. TB is treated by taking a combination of antibiotics for at least 6 months – rifampicin is just one of the antibiotics prescribed. Read more about TB.(external link)
Rifampicin is also used to prevent other infections such as meningitis or Haemophilus influenzae, if you've been in close contact with someone who has the infection. It may also be used to control itching for people with severe liver disease.