The characteristics of people who inject drugs in the United Kingdom: changes in age, duration, and incidence of injecting, 1980-2019, using evidence from repeated cross-sectional surveys

Abstract

Background and aims: Mortality and drug treatment data suggest that the median age of people who inject drugs is increasing. We aimed to describe changes in the characteristics of people injecting drugs in the United Kingdom (UK).

Design: Repeat cross-sectional surveys and modelling.

Setting: Low-threshold services in the United Kingdom such as needle and syringe programmes.

Participants: A total of 79 900 people who recently injected psychoactive drugs in the United Kingdom, recruited as part of the Unlinked Anonymous Monitoring Survey (England, Wales, Northern Ireland, 1990-2019) and Needle Exchange Surveillance Initiative (Scotland, 2008-2019).

Measurements: Age of people currently injecting, age at first injection, duration of injecting (each 1990-2019) and estimates of new people who started injecting (1980-2019).

Findings: In England, Wales and Northern Ireland between 1990 and 2019, the median age of people injecting increased from 27 (interquartile range [IQR], 24-31) to 40 (IQR, 34-46); median age at first injection increased from 22 (IQR, 19-25) to 33 (IQR, 28-39); and median years of injecting increased from 7 (IQR, 3-11) to 18 (IQR, 9-23). Values in Scotland and England were similar after 2008. The estimated number that started injecting annually in England increased from 5470 (95% prediction interval [PrI] 3120-6940) in 1980 to a peak of 10 270 (95% PrI, 8980-12 780) in 1998, and then decreased to 2420 (95% PrI, 1320-5580) in 2019. The number in Scotland followed a similar pattern, increasing from 1220 (95% PrI, 740-2430) in 1980 to a peak of 3080 (95% PrI, 2160-3350) in 1998, then decreased to a 270 (95% PrI, 130-600) in 2018. The timing of the peak differed between regions, with earlier peaks in London and the North West of England.

Conclusions: In the United Kingdom, large cohorts started injecting psychoactive drugs in the 1980s and 1990s and many still inject today. Relatively few people started in more recent years. This has led to changes in the population injecting drugs, including an older average age and longer injecting histories.

Keywords: Ageing; United Kingdom; demography; epidemiology; heroin; injecting; modelling.

FIGURE 1

Flow chart of study sample. UAM did not include consistent questions that allowed exclusion of people who inject image and performance‐enhancing drugs, though recruitment is intended to exclude such individuals. UAM, Unlinked Anonymous Monitoring; NESI, Needle Exchange Surveillance Initiative

FIGURE 2

Age of UAM participants, age at first injection of psychoactive drugs, and duration of injecting, by survey year. UAM, Unlinked Anonymous Monitoring

FIGURE 3

Duration of injecting among people who inject psychoactive drugs in England, Wales, and Northern Ireland, 1993–2019. Note: A similar figure for Scotland using data from NESI is provided in the Supporting Information. The pattern is similar with a peak of initiation in the mid‐late 1990s. NESI, Needle Exchange Surveillance Initiative

FIGURE 4

Modelled number of people injecting psychoactive drugs for the first time each year, with 95% prediction intervals

FIGURE 5

Sensitivity analysis of the effect of varying the assumed typical duration of injecting on the modelled number of people injecting for the first time each year in England (point estimates only)