currentsinbiology:

Recovery of dopamine function emerges with recovery from smoking

A new study in Biological Psychiatry
reports that smoking-related deficits in brain dopamine, a chemical
implicated in reward and addiction, return to normal three months after
quitting. The normalization of dopamine systems suggests smoking-related
deficits are a consequence of chronic smoking, rather than a risk
factor. These findings raise the possibility that treatments might be
developed that normalize the dopamine system in smokers.
                               

According to
first author Dr. Lena Rademacher, postdoctoral fellow at the University
of Lübeck in Germany, a major challenge in understanding
substance-related disorders lies in uncovering why only some individuals
become addicted.

Researchers think some people could possess a trait that predisposes
them to addiction, and suspect that brain circuits involving dopamine may be involved. Drugs of abuse release dopamine, and addiction to nicotine
is associated with abnormalities in the dopamine system. But
researchers are uncertain if smoking induces those abnormalities or if
they already exist and contribute to risk of nicotine addiction.