The number of young heroin addicts in England receiving treatment has dropped to its lowest recorded level, official figures suggest.
In 2011-12, 4,268 adults aged 18 to 24 started treatment, down from 11,309 six years earlier.
The National Treatment Agency for Substance Misuse (NTA) said "the sharp drop... is particularly encouraging".
Heroin users aged over 40 were the largest group in treatment, with more than 16,000 starting in the past year.
The latest figures come from NTA, an NHS special health authority dealing with the availability and effectiveness of drug treatment in England, in its report into long-term drug use and addiction trends.
Most addicts in treatment in England had taken heroin, with four in five of the 197,110 adults being treated for heroin or heroin and crack cocaine dependency.
A total of 96,343 were receiving help for heroin dependency while a further 63,199 were being treated for heroin and crack use.
The growing number of drug addicts over 40 was fuelled by an ageing population, rather than by new users, the NTA said.
NTA chief executive Paul Hayes said: "There's no evidence of swathes of people in their 40s and 50s beginning to use heroin and crack as they get older.
"It's a population that began using 20 or 30 years ago."
More over-40s are also dying from drug misuse, up to 802 last year from 504 in 2001, the figures showed.
Mr Hayes said: "Treatment needs to accelerate its recovery focus if more of the ageing heroin population are to successfully complete treatment and get their lives back on track.
"And we should be mindful that economic problems have historically exacerbated drug addiction."
Other NTA figures show:
- record numbers of drug addicts in England are recovering from addiction, with 29,855 successfully completing their treatment in 2011-12, up from 27,969 the previous year and almost three times the level of seven years ago (11,208)
- nearly one-third of users in the last seven years successfully completed their treatment and did not return (about 105,000 users out of 366,200)
- the number of new heroin addicts starting treatment for the first time has sharply reduced - from 47,709 in 2005-6 to 9,249 in 2011-12
Mr Hayes said: "The number of heroin and crack addicts is shrinking as fewer are starting to use the most harmful drugs, and more of them are recovering from addiction.
"The sharp drop in the number of young adults needing treatment is particularly encouraging."
Martin Barnes, chief executive of charity DrugScope, said the decline in heroin use and dependency among young adults was "perhaps a sign that drug treatment has been turning the tide of the heroin epidemic of the 1980s".
"We are, however, aware of the rising numbers of people over 40 in the treatment system, who often have particular needs around long-term and entrenched heroin use," he said.
"In difficult economic times, there is a strong and compelling case for national and local investment in drug and alcohol treatment."