Alcohol and drugs affect the brain’s neurotransmitters and neural pathways. At the same time, the brain strives to maintain balance. As a result, when drugs and alcohol change the brain’s chemistry, the brain adapts. Once the adaptation becomes the norm, the brain will want to “correct” an imbalance when the drug is no longer present by taking the drug again. Over time, substance use disorder changes both the brain’s structure and how it functions.