Background: Drug use indicators that are capable of measuring the individual levels of
harm following drug use, and in particular, poly-drug use, have previously been proposed, based on
individual drug and frequency of use data and expert rankings of harms related to various substances.
These indicators allow the estimation of risk profiles for selected groups of individuals and
comparisons, both over time and between populations. Recent advances regarding the ranking of
drug use harms allow a refinement of these indicators, separating the effects on self and others.
Objective: To define updated indicators and compare their performance to previous ones on datasets
related to the Italian ESPAD longitudinal data.
Methods: Two new scores, based respectively on the Harm to self and Harm to others substance
scores, are defined. These scores follow the same logic as the previous poly-drug score (PDS), but
now using the new Harm to self and Harm to others scores as weights, both in the individual calculations
and in the calculation of the two normalizing factors.
Results: The new harm-to-self drug use indicator is shown to correlate strongly with the previous
poly-drug use indicator; and the Harm to others indicator, is introduced and commented upon. Using
further ESPAD survey information related to personal behaviour, it is shown that high values of
poly-drug use indicators are linked to specific behaviours related to interest in school, relationship
with parents and use of leisure time. These results are consistent with previous analyses based on
surveys among high school students in Italy.