Chemotherapy is the administration of drugs that kill rapidly dividing cells such as leukemia or other cancer cells. Chemotherapy may be taken orally in pill or tablet form, or it may be delivered via a catheter or intravenous line directly into the bloodstream. Combination chemotherapy is usually given, which involves a combination of more than one drug. The drugs are given in cycles with rest periods in between. Sometimes, chemotherapy drugs for leukemia are delivered directly to the cerebrospinal fluid (known as intrathecal chemotherapy). Intrathecal chemotherapy is given in addition to other types of chemotherapy and can be used to treat leukemia in the brain or spinal cord or, in some cases, to prevent spread of leukemia to the brain and spinal cord. Side effects of chemotherapy depend on the particular drugs taken and the dosage or regimen. Some side effects from chemotherapy drugs include hair loss nausea, vomiting, mouth sores, loss of appetite, tiredness, easy bruising or bleeding, and an increased chance of infection due to the destruction of white blood cells. There are medications available to help manage the side effects of chemotherapy. Some adult men and women who receive chemotherapy sustain damage to the ovaries or testes, resulting in infertility. Most children who receive chemotherapy for leukemia will have normal fertility as adults, but depending on the drugs and dosages used, some may have infertility as adults.