studies exploring the association between COMT and addiction are mixed. Some studies failed to find evidence for an associations80; some indicate Val158 as the risk alleles and others indicate the Met158 alleles as the risk allele. The Val158 allele was found to be in excess among methamphetamine, nicotine, and polysubstance addicts.80–82 On the other hand, in addicted populations with high frequencies of internalizing disorders, such as late-onset alcoholics in Finland83 and Finnish social drinkers,84 increased risk appeared to be conferred by the Met158 allele.
