The number of heroin and crack cocaine users in England has fallen, according to independent research.
The study by the University of Glasgow shows there were about 25,000 fewer addicts in 2009-10 than six years ago.
Researchers carried out the work for the National Treatment Agency for Substance Misuse, which is preparing to publish the full details on Monday.
A spokesman for the agency confirmed the latest estimate of 306,150 opiate and crack cocaine users, of whom 103,185 were injecting.
The total is down from about 327,500 in 2004-5 and from a peak of about 332,100 in 2005-6.
Gordon Hay, who led the study, told The Independent newspaper that the latest estimate is the first statistically significant drop.
"It is going down more in younger age groups, both because they are less likely to use heroin and crack than the older age groups and because there are effective ways of dealing with them," he said.
Mr Hay said there had been a "massive expansion" of treatment.
The research follows a slight drop in the number of drug-related deaths in England and Wales.
The Office for National Statistics said last month that the total number of deaths caused by drug poisoning, including the misuse of illegal substances, was 2,747 in 2010 - a 5% drop on the previous year.
