You go to the prison doctor, show him your bruises and other injuries, and tell him you are feeling very ill and need hospital treatment. Unfortunately, the drugs mafia has bribed the doctor and so he refuses to give you a hospital bed, telling you you will be all right again in a couple of days.
Learn karate from a prison library book
Go to prison director and plead with him for protection
Take an overdose of drugs so that you are really ill