It's called "addiction," e.g.,

http://www.davidbrin.com/addiction.html

Get pierced or tattooed without anesthesia, get a happy flow of endorphins and enkephalins. Do it again and again. Or cut to the chase,

Google
wireheads niven 229 hits

Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz3.pdf