BACKGROUND:Housing instability contributes to poor health outcomes among people who inject drugs (PWID). Housing affordability in Montreal has declined since 2020. We described changes in the prevalence and spatial distribution of unstable housing among PWID. METHODS:We analyzed data from the HEPatitis COhort (HEPCO) of PWID in Montreal across three time frames: 2011-2014, 2015-2019, and 2020-2024. Housing was categorized as stable, precariously housed, or unsheltered based on the Canadian Observatory on Homelessness definition. Postal codes of primary residence over the past month were geocoded using the ggmap package in R. A threshold (median+2*median absolute deviation) was used to identify boroughs with increasing concentration of unstably housed PWID in 2020-2024 compared to 2015-2019. RESULTS:Among 1607 study visits (2011-2014: 552, 2015-2019: 547, and 2020-2024: 508), the proportion of unsheltered PWID increased to 41.3% in 2020-2024, vs. 26.1% in 2015-2019 and 27.4% in 2011-2014. In 2020-2024, 43.5% of PWID were stably housed vs. 51.4% in 2015-2019 and 53.8% in 2011-2014. Unsheltered PWID were mostly centralized in the downtown area, but precariously housed participants were more dispersed in their locations. We identified six boroughs with increasing concentrations of unstably housed (including precariously housed and unsheltered) PWID, mainly in downtown and adjacent boroughs. CONCLUSION:In the context of declining housing affordability, an increased proportion of PWID are reporting being unsheltered. Further work is needed to examine transitions from stable and precarious housing to being unsheltered. Services supporting precariously housed people may need to diversify their geographic locations, given this population's more dispersed residential profile.

Background: Severe mental illness (SMI - psychotic and bipolar disorders) is common among individuals with opioid use disorder (OUD). This study examined the impact of SMI on opioid agonist treatment (OAT) retention, and SMI and OAT on all-cause mortality. Methods: A retrospective cohort study of 14763 individuals receiving OAT for the first time in New South Wales, Australia, 2006-2017. OAT records were linked to hospital, mental health treatment, and custodial information. Multivariable Cox regression models were used to compare OAT cessation/retention and all-cause mortality among those with/without SMI, adjusting for potential confounders. Results: There were 1989 (13.5%) individuals with SMI and 763 (5.2%) deaths. The risk of treatment cessation during a first OAT episode was 16% higher for individuals with SMI [adjusted hazard ratio (aHR) 1.16, 95% confidence interval (CI) 1.09-1.23]. Among those with multiple OAT episodes, differences in retention between those with/without SMI were most notable in the first three treatment episodes; this difference was attenuated between episodes four to five. Although SMI increased mortality risk [aHR 1.35; 95% CI 1.14-1.60] and being in OAT decreased mortality risk [aHR 0.24; 95% CI 0.20-0.29], OAT status did not modify the effect of SMI on overall mortality risk. Conclusions: Comorbid SMI and OUD significantly reduces OAT retention during early episodes of treatment and is associated with increased mortality risk. There is no differential treatment effect on mortality among those with and without SMI. Interventions to identify, support, and engage individuals with SMI in OAT are needed early after commencing treatment.

BACKGROUND:Engaging people who inject drugs (PWID) in research is challenging due to stigma, distrust, and structural barriers. Peer-led recruitment may enhance reach and equity, yet few studies have quantitatively evaluated its outcomes. METHODS:Between Feb 2021-Dec 2023, a Partnerships Lead with Lived Experience implemented three new recruitment strategies within the HEPCO cohort study of PWID in Montreal, Canada. Strategies extended research activities into the community through a flexible engagement model comprising pop-up research clinics (n = 109 events), street outreach (n = 29 events), and community kiosks (n = 26 events). Peer-led recruitment pipelines and strategy efficiency were quantified, and enrolment outcomes compared with traditional recruitment methods (e.g., word-of-mouth). RESULTS:Peer-led strategies generated >2000 interactions with community members and contributed 46% of new enrolments despite substantially fewer operational days (164 vs 450 for traditional strategies). Overall efficiency was 0.88 new enrolments per recruitment event, with kiosks and street outreach nearly twice as efficient as pop-up clinics (1.31, 1.28, and 0.67 new enrolments/event). Participants recruited through peer-led strategies were more likely to report recent unstable housing (71.8% vs. 52.1%) and incarceration (19.1% vs. 12.1%) but not sex work (3.5% vs. 9.1%). Peer-led strategies enrolled slightly higher proportions of women (19.0% vs. 16.2%) as well as ethnically and linguistically diverse participants (14.8% vs. 11.4% non-White; 20.4% vs. 13.2% non-French preferred language). CONCLUSION:Peer-led recruitment engaged participants with greater structural vulnerability and modestly increased gender, ethnic, and linguistic diversity. Such approaches can strengthen equity in substance-use research when peer leadership is adequately resourced and embedded from the outset.

Overdose in Canada has been constituted as a 'crisis', with unprecedented mortality rates observed over the past decade. The origins of this situation have been located in opioid over-prescribing in the late 2000s, followed by increased diversion of opioids to the illicit market, then, beginning around 2015, a rapid market shift to highly potent synthetic opioids such as fentanyl. The present-day drug supply is characterised as 'toxic'. Despite considerable investment, and occasional brief declines in overdose deaths in some regions, mortality remains high nationally. Following Janet Roitman's work critically interrogating the stakes of crisis and what this concept enables, we ask what is being constituted as the overdose crisis in our field at this time and explore the effects of this claim. We examine how a focus on toxic drug supply shapes narratives regarding the boundaries and causes of the crisis - and also possible solutions. Drawing on epidemiological analyses of persistent growth in overdose deaths pre-dating the conventionally accepted beginning of the overdose crisis in Canada, we attend to how crisis is constituted through its evidence-making. By interrogating what is identified as being in crisis, and what crisis narratives afford in framing action and response, our analysis prompts critical reflection on how the claim to crisis operates as a theory for change. As a form of damage-centred narrative, crisis is no longer sufficient.

Importance:Individuals who experience opioid overdoses are at high risk of death, and data are limited about the comparative effectiveness of medications for this high-risk population. Objective:To compare the effectiveness of methadone and buprenorphine-naloxone in individuals with a past-year history of opioid overdose. Design, Setting, and Participants:This retrospective cohort study with target trial emulation included individuals who started methadone or buprenorphine-naloxone treatment between January 1, 2017, and December 31, 2023, in Ontario, Canada. Participants had a past-year emergency department visit for an opioid overdose and no use of either medication for 7 days. Individuals starting each medication were matched on a 1:1 basis using propensity scores, sex, and index date. Data were analyzed from November 2024 to June 2026. Main outcomes and measures:The primary outcome was death from any cause within 1 year, analyzed using an initiator approach with Cox proportional hazards regression. The secondary outcomes were opioid overdose and treatment discontinuation. Per-protocol analyses evaluating outcomes before medication discontinuation were also conducted. Results:A total of 5882 individuals were included in the matched cohort (mean [SD] age, 35.8 [10.8] years; 1888 female [32.1%]). In the methadone-initiating group, 165 individuals (5.6%) died within 1 year, compared with 210 (7.1%) in the buprenorphine-naloxone-initiating group (HR, 0.78; 95% CI, 0.63-0.95; P = .01), with an E-value of 1.9. Median time to treatment discontinuation was 25 days (IQR, 7-131 days) in the methadone group compared with 16 days (IQR, 5-69 days) in the buprenorphine-naloxone group (HR, 0.78; 95% CI, 0.74-0.82; P < .001). There was no significant difference in the time to first opioid overdose (HR, 1.07; 95% CI, 0.97-1.18; P = .17). In the per-protocol analyses, there was no significant difference in the hazard of death among individuals starting methadone and buprenorphine-naloxone (HR, 0.84; 95% CI, 0.48-1.47; P = .55) and an increased hazard of opioid overdose among individuals starting methadone (HR, 1.52; 95% CI, 1.19-1.93; P < .001). Conclusions and Relevance:In this matched cohort of individuals with a past-year opioid overdose, starting methadone was associated with a reduced risk of death during the subsequent year compared with starting buprenorphine-naloxone. Treatment durations were short, particularly among individuals starting buprenorphine-naloxone, and there was no significant difference in mortality during receipt of opioid agonist treatment. These findings may be explained by unmeasured confounding, and epidemiologic studies in other jurisdictions are needed to confirm these findings.

Ongoing monitoring of hepatitis C virus (HCV) and HIV incidence among people who inject drugs (PWID) is important for epidemic control and assessing progress towards disease elimination. We estimated trends in HIV and HCV infection incidence in a community-based cohort of PWID in Montreal, Canada. Data from March 2011 to March 2025 were drawn from the HEPCO study of PWID aged ≥ 18 years and living in Montreal. Participants with at least two visits were included in analyses. We used a random point approach to estimate the date of each infection event, imputing each date 1000 times, and Rubin's rules to pool incidence rates and 95% CIs across imputations. A total of 743 participants contributed to HCV analyses, with 152 infection events and incidence of 6.47 per 100 person-years (p-y) (95% CI 6.46-6.49). Incidence peaked in 2013 and declined to 2019 before increasing again post-pandemic. There were 61 primary HCV infection events (incidence: 6.15 per 100 p-y; 95% CI 4.79-7.90) and 91 reinfection events (incidence: 6.71 per 100 p-y; 95% CI 6.69-6.73). A total of 836 participants contributed to HIV analysis, with only eight infections over 3089.89 p-y (incidence: 0.26 per 100 p-y; 95% CI 0.13-0.52). Declining HCV incidence among PWID in Montreal may have reversed, but limited data collection during the years 2020-2021 complicates interpretation. HIV incidence was persistently low. HCV incidence remains above World Health Organization elimination targets, highlighting the need for sustained investment in prevention and linkage to care for PWID.

Background: Syphilis cases have increased among women and heterosexual men in Canada and people who inject drugs (PWID) are an emerging group at risk of infection. We aimed to examine syphilis prevalence among PWID stratified by men and women, and differences according to intersecting population groups, socio-structural factors and sexual and substance use behaviors. Methods: Data were from HEPCO, a community-based cohort study of PWID in Montreal. We tested for syphilis (lifetime and active) via treponemal testing reflexed to non-treponemal testing if positive. Odds ratios were estimated using bivariable exact logistic regression to examine differences in the prevalence of lifetime syphilis infection. Results: From November 2022 to March 2024, 386 people (16.1% women) had a syphilis test. Thirty-three people (8.6%, 95%CI 6.1,11.8) had evidence of lifetime syphilis infection, of whom two had active syphilis. Lifetime prevalence was significantly higher among men identifying as gay or bisexual, men with HIV, and those who reported recent sex work, condom-less sex, 2 or more sex partners and amphetamine injecting. Among women, prevalence was higher among those who reported recent sex work, recent unstable housing and amphetamine injecting; however, there was no statistically significant difference. Conclusion: Active syphilis infection was uncommon among this cohort of PWID; however, lifetime syphilis infection was almost 9%. Among men in this cohort, evidence indicates that syphilis intersects with other key population group characteristics. More data are needed to better understand syphilis among women who inject drugs. Periodic syphilis testing among PWID may be justified alongside testing for other sexually transmissible and blood borne infections.

INTRODUCTION:Evidence quantifying dimensions of stigma and their health impacts among people who inject drugs (PWID) remains limited. We characterized substance use-related stigma dimensions among PWID and estimated their associations with injection-related bacterial infections (IRBIs). METHODS:We conducted a cross-sectional study nested within a prospective cohort of PWID in Montréal (August 2024-November 2025). Substance use-related stigma was measured using the Substance Use Stigma Mechanisms Scale (SU-SMS), capturing three mechanisms (enacted/anticipated/internalized); enacted and anticipated stigma were further stratified by source (family/healthcare workers). Mean scores were computed for each dimension (range 1-5) and dichotomized as low (<4) or high (≥4); any stigma was defined as high if ≥1 mechanism was high. IRBIs in the past three months included skin/soft tissue infections, bone/joint infections, sepsis, or endocarditis. Associations with IRBIs were estimated for each stigma mechanism, and by source, using Poisson regression with robust standard errors. RESULTS:Among 377 PWID, high enacted, anticipated, and internalized stigma were reported by 10%, 10%, and 9%, respectively. High stigma on any mechanism was reported by 20%. By source, high family-related stigma was more prevalent than healthcare-related stigma for both enacted (30% vs 11%) and anticipated stigma (26% vs 12%). Recent IRBIs were reported by 23% of participants. Associations with recent IRBIs were strongest for enacted stigma, with those reporting high (vs low) levels twice as likely to report one (adjusted prevalence ratio [aPR]=2.1; 95%CI: 1.4-3.1); however, associations were modest and inconclusive for anticipated (aPR=1.3; 95%CI: 0.8-2.1) and internalized stigma (aPR=1.2; 95%CI: 0.7-2.2). When stratified by source, enacted stigma remained associated with IRBIs whether from family or healthcare workers, whereas anticipated stigma showed no clear association from either source. DISCUSSION:One in five PWID experienced high substance use-related stigma on at least one of the three mechanisms. Findings underscore the multifaceted, harmful impact of stigma on PWID health and the need to address stigma from both family members and healthcare workers.

BACKGROUND:Some evidence suggests the benefits of opioid agonist therapy (OAT) in preventing hepatitis C virus (HCV) acquisition are stronger in men than women. However, existing analyses have used crude OAT exposure measures. We compared HCV incidence and estimated the effects of OAT on HCV acquisition among women and men who inject drugs using granular OAT exposure data. METHODS:Data were from Montréal's Hepatitis Cohort (HEPCO) study, March 2011-March 2024. We estimated overall and gender-stratified HCV incidence rates and performed discrete-time survival analyses, overall and gender-stratified, to estimate the associations between OAT engagement and HCV acquisition. In multivariable analyses, we adjusted for age and incarceration. RESULTS:HCV incidence was similar in women and men, with a rate of 6.93 (95% CI 5.67, 8.46) per 100 p-y in men, and 7.84 (95% CI 5.13, 11.98) per 100 p-y in women. In the men's adjusted model of the association between OAT engagement and HCV acquisition (in OAT versus not in OAT (but eligible)), the aHR was 0.52 (95% CI 0.33, 0.83). Among women, the aHR was 0.89 (95% CI 0.30, 2.70). However, the confidence interval was wide and crossed the null in the women's model. CONCLUSION:We found similar HCV incidence among women and men who inject drugs in Montréal; however, among OAT-eligible men, OAT engagement was strongly associated with a lower risk of HCV acquisition. These findings highlight that gender disparities in HCV, as observed in some settings, are not consistent. Further research is needed to determine factors underlying gender differences.

INTRODUCTION:People who inject drugs may experience several non-viral injecting-related injuries and diseases (IRID), including skin and soft tissue infection (SSTI) and venous disease, often resulting from bacteria introduced via unsafe injecting practices or environments. Women are overrepresented among those reporting multiple and recent IRID. However, limited evidence exists about how gender interacts with known IRID risk factors. METHODS:Surveys were conducted 2009-2023 with approximately 900 Australians who inject drugs per year (N = 7538 total). Participants self-reported past-month drug use behaviours and IRID experience. We conducted multivariable binary logistic regression to determine the relationship between gender and SSTI and venous disease. To examine whether gender uniquely affected specific injecting risk behaviours with respect to SSTI and venous disease, two interaction terms were separately added: (i) gender and injecting frequency; (ii) gender and reuse of one's needles. RESULTS:Surveys were completed by 5038 men and 2500 women. Past-month SSTI was reported by 8% of the sample (95% confidence interval 7%-9%), with a higher proportion among women (10%) than men (7%). Overall, 4% reported past-month venous disease (95% confidence interval 3%-4%), a higher proportion among women (5%) than men (3%). Examining both outcomes, no statistically significant interactions between gender and needle reuse or injecting frequency were found. DISCUSSION AND CONCLUSIONS:Despite no statistically significant interaction between gender and reuse or injecting frequency, our study demonstrates a gender difference in exposure to risk factors associated with SSTIs and venous disease. Interventions to reduce SSTI and venous disease, particularly those deemed safe and appropriate by women, are needed.

Background:The relationship between substance use and chronic pain is bidirectional. Although chronic pain and polysubstance use are highly prevalent among people who inject drugs (PWID), few studies have examined how the frequency of use of different substances relates to chronic pain. Aims:The aim of this study was to examine associations between substance use frequency and chronic pain in a sample of PWID. Methods:A cross-sectional analysis was conducted among PWID participating in a community-based cohort in Montreal, Canada. Chronic pain measures were introduced in the interviewer-administered questionnaire in February 2017. The first questionnaire was used for analyses, which covers data up to November 2022. Logistic regression analyses were conducted to examine associations between alcohol, stimulants, opioid and cannabis frequency and chronic pain. Results:Six hundred and eight participants were included; 84% were men and mean age was 44.7 years old. Prevalence of chronic pain was 48%. Age (adjusted odds ratio [aOR] = 1.38, 95% confidence interval [CI] 1.15-1.65) and regular alcohol consumption in the past month (aOR = 1.76, 95% CI 1.13-2.75) were associated with chronic pain in univariable and multivariable logistic regression models. The frequency of use for all other substances was not found to be significantly associated with chronic pain. Conclusion:The prevalence of chronic pain in our sample was high. The positive association between high frequency of alcohol use and chronic pain could be explained by alterations of pain pathways by heavy use and withdrawal episodes, potentially increasing hyperalgesia. This study underscores the importance of addressing alcohol use along with other substances among PWID.

BACKGROUND:Bacterial sexually transmitted infections (STIs) are common among people in prison, a population identified by WHO as a key group to addressing the burden of sexually transmitted and blood-borne infections worldwide. To inform elimination efforts, we aimed to estimate the global prevalence of bacterial STIs (chlamydia, gonorrhoea, and syphilis) in prisons and other closed settings. METHODS:We conducted a systematic review and meta-analysis by searching online databases (MEDLINE, Embase, Global Health, PsycInfo, CINAHL, the Cochrane Database of Systematic Reviews, the Cochrane Central Register of Controlled Trials, Global Index Medicus, the Conference Proceedings Citation Index-Science, and the Conference Proceedings Citation Index-Social Sciences & Humanities) and reference lists for studies published from Jan 1, 2000, to Aug 5, 2025. We included peer-reviewed publications (scientific articles, conference abstracts, and technical reports) that reported on the prevalence of current chlamydia, current gonorrhoea, or current or previous syphilis infections, confirmed by validated diagnostic assays, among incarcerated populations (adolescents aged 10-19 years and/or adults aged >19 years). Two reviewers (GB and BH) independently assessed studies, extracted data, and evaluated the quality of studies using an adapted version of the Joanna Briggs Institute critical appraisal tool for prevalence studies. Pooled prevalence estimates for each bacterial STI were derived with use of generalised linear mixed-effects models, stratified by age group and, within each age group, by sex. Heterogeneity was quantified based on the I2 statistic and χ2 test. This systematic review and meta-analysis was registered with PROSPERO, CRD42023443370. FINDINGS:The search generated 5237 records, of which 212, corresponding to 206 unique studies, met the eligibility criteria and were included. Of the 206 studies, 137 included adults only (n=425 215), 53 included adolescents only (n=342 762), and 16 included both (n=675 119). 190 (92·2%) studies were conducted in high-income or upper-middle-income countries. Across the 206 studies, data were available for 1 443 096 individuals (483 438 [33·5%] females, 901 188 [62·4%] males, and 58 470 [4·1%] sex not reported). The mean age was 33·6 years (SD 9·7) for adults and 15·6 years (1·1) for adolescents. Among female adults, the pooled prevalence of current chlamydia was 6·5% (95% CI 5·1-8·3; I2=97·0%, p<0·0001; 15 582 crude infections in 166 767 females; 38 studies), the pooled prevalence of current gonorrhoea was 1·5% (0·8-2·7; I2=97·2%, p<0·0001; 4424 crude infections in 167 953 females; 32 studies), and the pooled prevalence of current or previous syphilis was 5·9% (4·1-8·3; I2=98·6%, p<0·0001; 5143 crude infections in 103 641 females; 59 studies). Among male adults, the corresponding estimates were 4·7% (3·7-6·0; I2=94·4%, p<0·0001; 7101 crude infections in 128 380 males; 33 studies), 0·4% (0·2-1·1; I2=98·4%, p<0·0001; 591 crude infections in 330 418 males; 23 studies), and 3·7% (2·8-5·0; I2=99·4%, p<0·0001; 10 404 crude infections in 522 133 males; 61 studies), respectively. Among female adolescents, the pooled prevalence of current chlamydia was 16·8% (14·0-20·0; I2=96·7%, p<0·0001; 31 206 crude infections in 221 350 females; 38 studies), the pooled prevalence of current gonorrhoea was 6·0% (4·5-7·9; I2=89·3%, p<0·0001; 2053 crude infections in 39 949 females; 22 studies), and the pooled prevalence of current or previous syphilis was 1·9% (0·1-26·4; I2=76·0%, p=0·0058; nine crude infections in 449 females; four studies). Among male adolescents, the corresponding estimates were 7·4% (6·3-8·8; I2=97·0%, p<0·0001; 15 122 crude infections in 231 606 males; 29 studies), 2·0% (1·4-2·7; I2=94·5%, p<0·0001; 1393 crude infections in 75 697 males; 17 studies), and 1·9% (0·5-6·5; I2=24·7%, p=0·26; 11 crude infections in 596 males; three studies), respectively. The overall quality of studies was moderate (118 [57·3%] of 206 studies) or high (88 [42·7%] studies). INTERPRETATION:The high prevalence of bacterial STIs in incarcerated populations, particularly among adolescents and females, highlights substantial public health gaps in bacterial STI prevention and treatment. Offering opt-out bacterial STI testing to all people in prison should be considered to accelerate elimination efforts. FUNDING:None.

This cohort study uses target trial emulation to explore the comparative effectiveness of buprenorphine-naloxone and methadone for opioid overdose among youths in Canada.

This study uses Canadian administrative data to evaluate 1-year mortality among opioid overdose survivors in Ontario, Canada, and characterize postoverdose mortality risk after the widespread availability of fentanyl.

BACKGROUND:Overdose deaths in Canada have been rising since 2016, but long-term trends remain poorly characterized. We examined national overdose mortality trends from 1974 to 2023 and explored differences by sex, age, and province. METHODS:We conducted a retrospective analysis of accidental and undetermined-intent poisoning deaths in the Canadian Vital Statistics Death Database, calculating crude mortality rates (CMR) using Statistics Canada population estimates. We used segmented regression to model temporal trends and calculated average annual percentage change (AAPC) for each resulting segment. Analyses were stratified by sex, age (<25, 25-44, 45-64, and ≥65), and province. RESULTS:Between 1974 and 2023, 80,944 overdose deaths were recorded. Segmented regression of CMR revealed three phases: a period of relative stability (AAPC: -0.28 %; 1974-1991), followed by two accelerations (AAPC: 5.46 %; 1991-2013 and AAPC: 12 %; 2013-2023) CMRs were similar by sex until 2013-15, then surged in both males (AAPC: 13.81 %; 2012-2023) and females (AAPC: 9.32 %; 2015-2023). Rates in youth (<25) were stable until the early 2000s, then rose sharply (AAPC: 30.62 %; 2014-2017) before slowing, while rates among adults aged 25-44 (AAPC: 13.59 %; 2012-2023), 45-64 (AAPC: 11.56 %; 2014-2023), and ≥65 (AAPC: 18.48 %; 2020-2023) increased in recent years. Rates increased the most in Western provinces compared to Quebec and the Atlantic provinces. CONCLUSIONS:Canada's overdose epidemic reflects a segmented trajectory, with marked accelerations in 1996 and 2013, driven by healthcare practices, evolving drug markets, and social vulnerabilities. Regional and demographic disparities underscore the need for targeted, historically informed public health strategies.

Background:The age of people who inject drugs appears to be increasing in some high-income countries. We aimed to explore trends in the age of people injecting and recently starting to inject drugs in Australia, and to model incidence of initiation over time. Methods:We obtained data from the Illicit Drug Reporting System (IDRS) and the Australian Needle Syringe Program Survey (ANSPS), which comprise annual cross-sectional surveys with people who inject drugs (2000-2019). Outcome measures were current age, age of initiation, and time since initiation (both surveys), and drug first injected (IDRS only). We estimated time trends in age using quantile regression. We used the relative number of people initiating injecting drug use each year and existing population size estimates to model incidence of initiation. Findings:In total, 58,465 interviews with people who reported injecting drugs in the past month (33.7% women) were included. In both surveys, the median age increased over the study period (IDRS: 28-43 years; ANSPS 28-44 years). The median time since initiation also increased over the study period (IDRS: 8-22.5 years; ANSPS: 9-24 years), and the median age of initiation increased with calendar year of initiation (IDRS: 18-34 years; ANSPS: 20-30 years). Women tended to be younger and commence injecting drug use at a younger age than men. Modelling suggested that similar numbers of people injected drugs for the first time each year from 1980 (national estimates of 15,570 and 17,020 new initiates using IDRS and ANSPS data, respectively) to 1996 (IDRS: 16,360; ANSPS: 22,300 new initiates), followed by a decisive decline in incidence until 2012 (IDRS: 1110; ANSPS: 1830), whereafter it has fluctuated but remained low. Meth/amphetamine was consistently the predominant drug injected at initiation among IDRS participants, although there were peaks in heroin as the drug injected at initiation in the early 1980s and mid-1990s. Interpretation:In 2019, most people who were injecting drugs in Australia were part of a cohort that began injecting in the 1980s or 1990s. Consequently, the population was older and had been injecting drugs for longer compared to those injecting drugs in 2000. This has implications for health service delivery to people who inject drugs, with increasing age likely to be accompanied by a rise in chronic health conditions and an increase in injecting duration potentially resulting in higher incidence of injecting-related injuries and diseases. Funding:Australian Government Department of Health and Aged Care.