Number of people in opiate substitution treatment
It is important to know how many of the drug users in an area are receiving opiate substitution treatment (OST) because for heroin dependent injectors, being prescribed opioids is known to have a significant impact on injecting.

Dependent heroin users who enter opiate substitution treatment programme – and are prescribed an adequate dose – make significant reductions in the frequency of injecting, and may even stop injecting altogether.

When injecting does happen in those receiving OST, it is generally more planned and less 'desperate' because it is not usually driven by the onset of withdrawal, which the OST is aimed to prevent. This means that OST usually reduces the number of occasions on which blood borne virus transmission can occur.

When entering this figure it is important to use the relevant estimate for the number of people in OST at any one time rather than the figure for total number who pass through the treatment system in a year.

To see how substitution treatment impacts on needle and syringe coverage try completing the coverage calculator with 50% of injectors in treatment, and then again with none.