In the United Kingdom, University of Cambridge researchers have discovered that those who lack the neurotransmitter dopamine, at the top of the brain stem, are predisposed to compulsive behavior including drug addiction. The study conducted with rats and cocaine made a link between impulsive and compulsive behavior.

 Positron emission tomography (PET) scans were used on the rats and found that the impulsive and compulsive rats had 10-percent fewer dopamine receptors than did the normal rodents. The value of this study in drug addiction treatment is that by knowing this brain neurotransmitter vulnerability, medical researchers can now devise more targeted drugs for addicts.