"There is evidence from published and unpublished observational studies that opiate substitution treatment is associated with an average 54% reduction in the risk of new HIV infection among people who inject drugs. There is weak evidence to suggest that greater benefit might be associated with longer measured duration of exposure to opiate substitution treatment. All of the eligible studies examined the impact of methadone maintenance treatment, indicating that there are few data regarding the impact of buprenorphine or other forms of non-methadone opiate substitution treatment in relation to HIV transmission. We found no evidence that methadone detoxification is associated with a reduction in the risk of HIV transmission."

Source

MacArthur, Georgie J., et al., "Opiate substitution treatment and HIV transmission in people who inject drugs: systematic review and meta-analysis," BMJ 2012; 345 doi: http://dx.doi.org/10.1136/bmj… (Published 4 October 2012).
http://www.bmj.com/content/34…