Pilot studies in London and the south east and the north of England began last year.
Last week, deputy chief constable Howard Roberts of Nottinghamshire Police called for heroin addicts to be prescribed diamorphine on the NHS.
He called for consideration of wider use of diamorphine therapy. This would cost up to £12,000 per patient annually, compared with £3,000 for methadone. This could prove cost-effective because many addicts steal up to £45,000 a year to supply their habit, said Mr Roberts.
Dr Chaand Nagpaul, a member of the GPC prescribing subcommittee, said that any GP treatment of drug misuse should be as an enhanced service.
