Amphetamine type stimulants (ATS) have become the focus of increasing attention worldwide. There are understandable concerns over potential harms including the transmission of HIV. However, there have been no previous global reviews of the extent to which these drugs are injected or levels of HIV among users. A comprehensive search of the international peer-reviewed and grey literature was undertaken. Multiple electronic databases were searched and documents and datasets were provided by UN agencies and key experts from around the world in response to requests for information on the epidemiology of use. Amphetamine or methamphetamine (meth/amphetamine, M/A) use was documented in 110 countries, and injection in 60 of those. Use may be more prevalent in East and South East Asia, North America, South Africa, New Zealand, Australia and a number of European countries. In countries where the crystalline form is available, evidence suggests users are more likely to smoke or inject the drug; in such countries, higher levels of dependence may be occurring. Equivocal evidence exists as to whether people who inject M/A are at differing risk of HIV infection than other drug injectors; few countries document HIV prevalence/incidence among M/A injectors. High risk sexual behaviour among M/A users may contribute to increased risk of HIV infection, but available evidence is not sufficient to determine if the association is causal. A range of possible responses to M/A use and harm are discussed, ranging from supply and precursor control, to demand and harm reduction. Evidence suggests that complex issues surround M/A, requiring novel and sophisticated approaches, which have not yet been met with sufficient investment of time or resources to address them. Significant levels of M/A in many countries require a response to reduce harms that in many cases remain poorly understood. More active models of engagement with M/A users and provision of services that meet their specific needs are required.