Most of addiction is caused by one or more mutations that result in a lower than normal amount of dopamine stimulating the reward center (dopamine from the ventral tegmental area stimulating the nucleus accumbens).
ADDICTION IS A DISEASE Most addiction is caused by low dopamine levels in the nucleus accumbens, the brain’s pleasure center. All addictive drugs and behaviors raise dopamine levels at the nucleus accumbens. If they do not, they are not addictive.
WHY DO SOME PEOPLE GET ADDICTED? Dopamine tone at the nucleus accumbens is the reason we do anything twice. Individuals with low dopamine tone at the nucleus accumbens find that certain chemicals (addictive drugs) and/or behaviors (gambling/sex) increase dopamine concentrations to normal levels.
WHY DO SOME PEOPLE STAY ADDICTED? The drive to maintain dopamine levels is mediated by multiple chemical substances in the brain interconnecting the frontal lobes, midbrain and hindbrain. The midbrain dictates certain behaviors obscuring the logical thought processes from the frontal lobes. People who are addicted cannot control their need for drugs and alcohol despite negative health, social or legal consequences.