In 2003 the Thai government announced a radical shift in drug policy with the implementation of a War on Drugs. Although consequences of this controversial measure (e.g. drug dealer deaths) have received widespread attention relatively little work has evaluated changes in substance use. We used two anonymous representative samples of secondary school students to compare drug use in Northeast Thailand before (1998; n=4217) and after (2004/5; n=3489) the War on Drugs. Results indicate that reported levels of current illicit drug use reduced significantly between 1998 and 2004/5 (for methamphetamine from 4.2% to 0.9%). By examining trends in year of first methamphetamine use we identify that observed reductions in drug initiation are temporally consistent with the War on Drugs. However, while prevalence of alcohol use has also fallen, there was a three-fold increase in daily alcohol use. We suggest that this rise, combined with other negative impacts of 'wars' on drugs, means drug control requires a public health perspective that sees eliminating drug use as part of a wider strategy that has improvement in population health, not just drug prevention, as its core objective.