The first time people use drugs, it’s usually a conscious decision they’ve made. But once people become addicted, they are dealing with a brain disease. Each drug of abuse has its own individual way of changing how the brain functions. But in most cases, it doesn’t really matter which drug a person is addicted to; many of the effects it has on the brain are similar. The fact is that our brains are wired to make sure we will repeat activities, like eating, by associating those activities with pleasure or reward. Whenever this reward circuit is activated, the brain notes that something important is happening that needs to be remembered, and teaches us to do it again and again, without thinking about it. Because drugs of abuse stimulate the same circuit, we learn to abuse drugs in the same way. So while the initial decision to take drugs is a choice for some, a physical need replaces that choice. This is what’s known as addiction.