At one time scientists believed that experience of pleasure was enough to prompt people to continue seeking an addictive substance or activity. Recent research now proposes that the situation is a little more complicated than that. Dopamine contributes to the experience of pleasure, but it also plays a role in learning and memory- which are two key elements in the transition from liking something to becoming addicted to it. Dopamine networks with another neurotransmitter, glutamate, to take over the brain’s system of reward –related learning. This system has an important role in satisfying life because it links activities needed for human survival (like eating) with pleasure and reward. Addictive substances and behaviors stimulate the same circuit – and then overload it. When an addictive substance is exposed repeatedly, it causes the nerve cells in the nucleus accumbens and the prefrontal cortex to communicate that pairs liking something with wanting it – which in turn, drives us to go after it. This whole process stimulates us to take action in seeking out the source of pleasure, also known as the learning process.

Over time, the development of tolerance kicks in. As a result, dopamine has a less impact on the brain’s reward center. In time, people who have an addiction find that the desired substance doesn’t give them the same pleasure, which means the addict would have to take more of the same dopamine “high” because their brains have adapted.

Compulsion ends up taking over, and the wanting persists because the memory of the desired effect needs to be recreated. This causes intense cravings, which not only subsidize to addiction but to also to relapse after a hard-won sobriety. (Helpguide.org)