Drug users seeking help to quit their habit face a "postcode lottery" of care, a watchdog has said.
Drug action teams are in place to help people stop using drugs
The Healthcare Commission and the National Treatment Agency for substance misuse reviewed the services provided across England.
Services in general were found to be improving, but it was found that fewer than a third of dedicated action teams provided a good or excellent service.
The charity Drugscope said the report showed improvements were needed.
The report looked at whether the 149 drug action teams (DATs) prescribe drugs safely and appropriately and looked at their planning and co-ordination of services.
DATs are made up of people from NHS trusts, social services, the police, the probation service, and the voluntary sector.
In all, 5% of DATs were rated as excellent, 23% as good, 71% as fair and 1% as weak.
More seeking treatment
The report said DATs still needed to tackle a range of problems, including the need to keep people in treatment for longer.
While research has shown drug users fare better if they remain in treatment for at least 12 weeks, in 2004/05 only 53% were there for that amount of time.
It was found that while most DATs were improving on those rates, some were still underperforming.
The report also said there needed to be improvements on methadone prescribing for heroin addicts and for closer supervision in the early stages of treatment.
It said half of DATs were weak in giving patients an adequate care plan and almost three quarters were weak when it came to assessing and managing the risks for patients.
However, more people are now using drugs services.
Around 160,000 people joined treatment programmes in 2004/05, compared with 85,000 in 1998/99 - a rise of 89%.
Waiting times for treatment have also fallen from an average of 9.1 weeks in December 2001 to 2.4 weeks in September 2005, the commission said.
'Held to account'
Anna Walker, chief executive of the Healthcare Commission, said: "The number of problem drug users accessing treatment has increased dramatically in recent years, and that is good news.
"However, we now need to focus on improving quality.
"It is important that service users get the best treatment wherever they are and that they are encouraged to stay in treatment long enough to stabilise their condition.
"This review highlights excellent as well as poor practice, allowing the poorer performers to learn from the best."
Paul Hayes, chief executive of the National Treatment Agency, said the review would help it focus its work on failing areas.
Martin Barnes, chief executive of the charity Drugscope, said: "It is right that treatment providers are being held to account in the delivery of services for drug users, and much-needed improvements are being made.
"Clearly, however, the commissioning and management of services must improve if best practice and value for money are to be achieved across the board, especially within the NHS."
Shadow health minister, Tim Loughton, added: "In too many cases access to timely and sustainable treatment remains a lottery and these services are now very vulnerable to deficits amongst PCTs."