 Cigarette smoking is more prevalent among Veterans 27 than the general U.S. population 21. Smoking is common among people who use marijuana or caffeine heavily, and the use of menthol cigarettes is becoming increasingly common, affecting approximately 9 of the Veteran population. Recent research by the group and others indicates that heavy marijuana or caffeine use, or the use of predominantly menthol cigarettes, can alter brain nicotinic acetylcholine receptor nAChR densities. For the proposed study, brain imaging with PET scanning will be used to determine nicotine receptor densities in Veteran cigarette smokers with and without heavy marijuana or caffeine use, and in menthol and non-menthol Veteran smokers. Results of the proposed research may have implications for improving treatments for Veterans who smoke cigarettes and who have specific drug use co-morbidities or who use menthol cigarettes. 