The investigators speculated that the reduced blood ALDH activity in smokers was not caused by nicotine or any of its metabolites, but more likely, by components formed during the combustion of tobacco. In combination, these studies suggest that the biological mechanism underlying the association between cigarette use and alcohol use GR 144053 trihydrochloride disorder cannot be automatically extrapolated to the relationship between smokeless tobacco use and alcohol use disorder. More research is needed to uncover the underlying mechanism. The present study did not identify a significant relationship between possession of any mood disorder and smokeless tobacco use, consistent with a previous report in the USA, but inconsistent with a Finnish adolescent longitudinal study that found that early onset depressive disorders predicted two times the risk for smokeless tobacco use three years later. These inconsistent findings could be attributable to study design, difference in controlling for confounding effects, and different cultural factors that exist between Finland and USA. The GW 542573X finding of an association between inhalant/solvent use disorder and exclusive chewing tobacco is quite novel. People who had a lifetime diagnosis of inhalant or solvent use disorder are three times more likely to chew tobacco than those without inhalant/solvent use disorder. Previous studies have shown that inhalant abuse is usually initiated during preadolescence and chewing tobacco often begins in adulthood. Therefore, people with a history of inhalant abuse may be at high risk for chewing tobacco at some point in their life. Our novel finding may inform the primary prevention effort for chewing tobacco use. Future research that uses a prospective design is needed to confirm our hypothesized pathway. Dual use of snuff and chewing tobacco versus exclusive use of one of the two types of smokeless tobacco has not been investigated previously. The present study found that both panic disorder and specific phobia were associated with greater odds of exclusive chewing tobacco rather than exclusive snuff use and dual use of both smokeless tobacco products. These findings suggest that chewing tobacco is specifically linked to panic disorder and specific phobia. In addition, schizoid and antisocial personality disorder is less likely to be associated with exclusive use of snuff and chewing tobacco, respectively, than dual use. These results may inform secondary prevention of smokeless tobacco use. Depending on different types of smokeless tobacco used, one or two particular psychiatric comorbidities should be taken into account during the treatment.