The MIXTP program developed by authors was available to achieve the estimates of population size under the mixture of truncated count models via FORTRAN POWERSTATION and now it is available on the request. Table 3 illustrated the sizes of drug users, estimated by the mixture of truncated Poisson models and classified by types of drugs in Thailand 2005-2007. Methamphetamine users were the biggest group and tended to increase from 2005-2007 while heroin users trended to decrease slightly because of its high price. The numbers of marijuana, kratom-plant, and inhalant users were under-estimated because of their mild severities. Trend of marijuana sizes increased from 2005-2007 while trends of kratom-plant, inhalant, and others were difficult to predict.