Table 2 provides an overview of the outcomes assessed across the three studies. Study 1 will involve describing trends in the drug supply market of illicit PDPM using law enforcement drug seizure and detention data. Consistent with the EMCDDA, we will report on the number of drug seizures, allowing for comparison with other European countries.18 Number of seizures represents the best indicator of trends for the illicit supply of drugs, as quantities seized is vulnerable to variation from large individual seizures.20 This study will also include two repeated cross-sectional studies of prescribed medications dispensed to people (1) eligible for the GMS in the community and (2) in prison during the observation period. Monthly prevalence rates for PDPM (individual drugs) per 10 000 GMS eligible population and per 10 000 prison population (drug class and individual drugs) will be presented with 95% CIs. Median and IQRs of monthly prevalence rates and quantity dispensed will be reported overall, and by gender and age group.
Study 2 will report on patterns of use of PDPM, using anonymised individual level data from the three national drug and alcohol surveys. The weighted prevalence of past-year sedative and tranquiliser use, and opioid use (excluding heroin) will be calculated for each survey year, with 95% CIs. Estimates of self-reported use will be reported by age, gender and geographical locations. Sampling weights will be used in all analyses. These weights adjust estimates for excluded populations and survey nonresponse.21
Annual detection rates for PDPM in MBRS data will be calculated as the number of positive screenings per 1000 tests, and per 10 000 licenced drivers. Similarly, annual detection rates postmortem will be calculated per 1000 postmortem cases (by drug class, and where possible by individual drug). Detection rates among people attending the NDTC will be calculated as the number of people with at least one positive screening (by drug class) per 1000 adults attending the NDTC.
Study 3 will provide detail on the health burden associated with the use of PDPM. Using anonymised individual level data from the NDRDI, annual standardised drug-poisoning death rates involving PDPM will be calculated per 10 000 population. Standardised mortality rates for each year of the study period will be calculated per 10 000 population, standardised to the European Standard Population. Anonymised data from the National Self-Harm Registry will be used to calculate annual rates of intentional non-fatal overdose presentations involving PDPM (alone and in combination with other drugs and/or alcohol) per 10 000 population, per 1000 self-harm presentations, and per 1000 intentional drug overdose presentations between 2010 and 2020. Finally, using anonymised records from the NDTRS, we will calculate annual prevalence rates of treatment demand for problem drug use involving PDPM (alone and in combination with other problem drugs) per 10 000 population, and per total number of cases seeking treatment from 2010 to 2020.