Porn, too, is a superstimulant. A user can see more nubile young females (or whatever gets him going) in an afternoon than his hunter gatherer forbears would have seen in a lifetime. Porn makers "lace" their products with domination, violence, risky and forbidden acts precisely to enhance their addictiveness.
People often have no idea they're hooked until they try to stop using, and suffer intense withdrawal symptoms (shakes, anxiety, depression, insomnia, overwhelming horniness that is far greater than their pre-porn libido, etc.). See "Three Myths about Porn."