BACKGROUND: Medically Supervised Injecting Facilities (MSIFs) are locations where illicit drugs can be injected using sterile equipment under professional supervision. They aim to reduce risks associated with public injecting and injecting alone such as overdose and related harms. Evidence shows that MSIFs reduce overdoses, public injecting and related litter, and increase service engagement. Ireland's first MSIF opened in December 2024. The study assesses its impact during its first four months.

METHODS: All publicly accessible areas within 500 metres of the facility were patrolled weekly before and after it opened (September 2024-April 2025). Discarded needles, crack pipes, public injecting, loitering, and weight of discarded items were recorded. Weather data was controlled for and client uptake (number of unique clients using MSIF) was obtained. Generalised linear models and bivariate correlations compared pre and post changes.

RESULTS: Attendance increased almost fivefold during the study period. The average number of discarded needles per patrol decreased by 20 % (from 3.14 before to 2.50 after, p = 0.288). Each additional client attending was associated with a 5 % reduction in discarded needles (IRR = 0.95, 95 % CI: 0.92-0.99, p = 0.008). Crack pipes declined by 20 % (p = 0.545), with a 59 % reduction in the weight of drug-related litter (p < 0.001). Loitering declined by 45 % (p = 0.002) while public injecting remained rare (one before, one after).

CONCLUSIONS: Early evidence suggests community level benefits after four months including reduced drug-related litter and public loitering. Continued monitoring is required to assess long-term impact.