Dopamine plays a major role in the brain system that is responsible for reward-driven learning. Every type of reward that has been studied increases the level of dopamine transmission in the brain, and a variety of addictive drugs, including stimulants such as cocaine, amphetamine, and methamphetamine, act directly on the dopamine system. Dopamine surges when a person is exposed to novel stimuli, particularly if it is sexual, or when a stimuli is more arousing than anticipated. Because erotic imagery triggers more dopamine than sex with a familiar partner, exposure to pornography leads to “arousal addiction” and teaches the brain to prefer the image and become less satisfied with real-life sexual partners.
— Joe Carter