Use of opioid substitution therapy (OST), with or without a needle syringe program (NSP), appears to reduce the number of people who inject drugs and develop hepatitis C compared with no OST use (no absolute numbers per 1000 were available; on average, reduction was 50% with OST vs no OST, and 55% with OST plus NSP vs no OST plus low or no NSP). NSP alone shows no clear differences between groups overall (low vs no NSP coverage, or high vs low/no NSP), although subgroup analyses based on region suggest that fewer people in Europe may develop hepatitis C with high NSP than with low/no NSP coverage (on average, reduction was 76%). When assessed, the quality of evidence was very low to low. No firm conclusions can be drawn.