A drug used to treat epileptic seizures and bipolar disorder and to prevent migraine headaches. It is also being studied in the treatment of several types of cancer. It blocks an enzyme that cells need to grow and may cause cancer cells to die. It also blocks the growth of new blood vessels that tumors need to grow. It is a type of anticonvulsant, histone deacetylase (HDAC) inhibitor, antimaniacal, migraine headache prophylactic, and antiangiogenesis agent. Also called Depakene and valproic acid.