The purpose of the study is to determine if bupropion is can help people reduce or stop their methamphetamine use and to investigate whether genetic variations influence whether people respond to treatment with bupropion for methamphetamine addiction, which may help doctors and patients better decide if treatment with bupropion will be beneficial or not. To identify possible genetic variations that influence response to bupropion, we will perform genetic tests on blood or saliva specimens from participants receiving treatment with either bupropion or placebo (which is a pill that contains no medication) in conjunction with standard cognitive behavioral therapy drug counseling. We will compare methamphetamine use, as assessed with urine drug screens, among participants receiving bupropion versus those receiving placebo to determine if bupropion helps people to reduce or stop their methamphetamine use. We will then compare the results of the genetic tests among participants who respond and who do not respond to bupropion. In addition, since the amount of methamphetamine a person uses was associated with response to bupropion in preliminary studies, we will also compare the results of genetic testing among persons with heavy versus light methamphetamine use before entering treatment.