A study published earlier this year that concluded supervised drug injection sites may not be as effective in preventing drug overdose deaths as previously thought has been retracted, Vox reports.

The analysis, published in the International Journal of Drug Policy, concluded supervised injection sites have no significant effect on overdose deaths and syringe sharing. The sites are linked to a small reduction in drug-related crimes, the study found.

The researchers said out of the dozens of studies done on supervised injection sites, they could find only eight that were rigorous and transparent enough to include in their analysis. They called for more studies to be done to reach a more definitive conclusion.

The journal announced it was retracting the study because of serious methodological flaws in how it evaluated outcomes. The study combined outcomes for mortality, drug-related crimes, sharing of drug equipment, and problematic drug use. Each of these outcomes could be affected differently by a supervised drug site, according to experts who wrote critical reviews that led to the study’s retraction.