Effects of Metformin During Nicotine Withdrawal

There is a need for novel approaches to optimize smoking cessation treatment to help more smokers quit. Mood disturbance and cognitive deficits during nicotine withdrawal may be important treatment targets given their association with smoking relapse. In addition, factors such as HIV-1 infection may exacerbate abstinence effects on mood and cognitive deficits and thus should be measured and controlled for. The investigators hypothesize that the FDA-approved medication, metformin, will attenuate withdrawal-related mood disturbance and cognitive deficits, controlling for HIV status. Using a well-validated abstinence challenge paradigm, the investigators propose a placebo-controlled double-blind parallel arm study with one between-subjects factor of medication (low dose: 500 mg, high dose: 1500 mg, and placebo). Non-treatment seeking smokers (HIV-: n=54; 18 per group) will complete this 23 day study.