In laymen's terms, the brain is a structure which reacts to internally produced chemicals. These chemicals, called neurotransmitters, are the mediators of the instincts for survival, reproduction, and interpreting the external environment through impulses from sensory organs. In the case of substance abuse and addiction, the removal of external chemicals through abstinence, after detoxification, is essential in treatment and recovery. In the disease of addiction, after exposure to external chemicals, the complex processes are permanently distorted and thus the return to normal drinking, drug use, or other chemical use is impossible. All drugs and chemicals used in addicted individuals must be thoroughly supervised by some healthcare worker who knows the biochemical interactions involved.
Denial is the hallmark symptom of addiction.
As one can see, the normal chemical responses in the brain are synchronous with external circumstances. The sight or sensing of an approaching train at high speed produces fright and ultimately flight, hopefully. If the internal chemical environment and the external environment no longer correlate, that is, for example, the brain is bathed in a sedative drug such as alcohol, it fails to identify the danger of the approaching train and the entire organism reacts in denial of the impending danger and disruption. Since denial is an internally mediated chemical reaction, it is different from lying, and it is not a voluntary response. It is as important as total abstinence from all mind-altering drugs in recovery.