Functioning across several life domains, in the first cohort of illicit heroin users to be prescribed injectable diamorphine (pharmaceutical heroin) as an adjunct to treatment within a community drugs service, was assessed in a cross-sectional study with a 6-month follow-up. Case-control matching procedures were employed to compare outcomes in this group with an oral methadone-prescribed sample, attending different clinics within the same community service and geographical locale. The Heroin Prescribed (HP) group manifested lower levels of psychopathology and showed greater retention in treatment. Although reduced, illicit heroin misuse was not eliminated; the use of other illicit substances was comparable between groups but significantly more of the HP group were using illicit cocaine. Although no differences in current physical health were apparent, the sharing of used injecting equipment was reported only in the MP group. Criminal activity appeared significantly reduced, but not eliminated, in the HP group. Implications for prescribing practice are discussed.