What are the biochemical effects of drug addiction on brain?

Wow, good question!: Boy, that's a tough question! even tougher to answer with only 400 characters! drug addiction effects the brain "biochemically" by causing certain receptors to change their behavior---either by increasing or decreasing the activation of the neurotransmitters. This is the exact reason why addiction is called a disease--a person cannot control what happens to the receptors no matter what!

Affects judgement: Addiction to stimulants "is often linked to excessive risk taking, sensation seeking, and impulsivity, but in ways that are poorly understood, " write dalley and colleagues.