Our analyses show that the number of treatment units contributing to the TDI varies greatly between countries and over time. The large gaps in treatment rates far exceed the variation that would be expected based on prevalence of use and of CUD, questioning the validity of the estimates across time and space. Moreover, up-to-date information on TDI coverage, i.e., the share of all relevant treatment units covered in each country, is not available. Thus, we recommend that between-country comparisons should not be undertaken without accounting for methodological differences. Further, an increase in treatment rates can reflect a number of different factors (in addition to treatment demand itself), such as TDI reporting completeness or quality, a higher willingness of users to seek treatment, or increased availability of treatment. We recommend that, where feasible, improvements to TDI data quality should be made to facilitate understanding of true treatment demand and enable robust estimates of change.
