What will crack cocaine do to you if it is not used for medical reasons?

There is no medical use for crack. There is a medical use for regular cocaine -- it is used as an anesthetic in eye surgeries -- but not crack cocaine.

Crack is a highly addictive drug (as is regular cocaine). Although it is not physically addictive (there are no physical withdrawal symptoms) it is highly psychologically addictive (meaning, it causes your brain to crave more of it). It is nearly impossible to do crack without becoming addicted to it.

Smoking crack causes you to lose all your inhibitions and judgment, so that you will do anything -- like steal or prostitute yourself -- to get more of it. Sometimes crackheads are called "chickenheads." This is because, when you run out of crack, the craving to do more is so irresistible, that you may find yourself down on your hands and knees on the floor, searching for any tiny pieces of crack that you may have dropped. People who do this look like chickens pecking at the ground, and thus are called "chickenheads."

Smoking crack also destroys your lungs.