Name a common side effect of rifampin.

Rifampin is an antibiotic commonly used to treat infections such as tuberculosis and is known for its distinctive side effect of causing an orange discoloration of bodily fluids. This includes urine, sweat, tears, and even contact lenses. The orange color is due to the drug's chemical properties and its metabolites, which are excreted in body fluids. This side effect is generally harmless and is a result of rifampin's mechanism of action and metabolism, but it can be surprising to patients who may not have been informed beforehand.

The other choices are potential side effects of various medications but are not specifically characteristic of rifampin. Headaches can occur with many drugs, thrombocytopenia is a more serious side effect associated with a different class of medications, and diarrhea can result from antibiotics due to changes in gut flora but is not specifically associated with rifampin as a common or defining side effect. Therefore, the orange discoloration of bodily fluids stands out as a key and specific side effect related to rifampin use.