Drug action teams in England are not referring enough addicts to residential treatment schemes, it has been claimed.
Drug action teams are in place to help people stop using drugs
The Association of Directors of Social Services is warning of an impending crisis, and says some providers could close down altogether.
It is thought addicts are instead being referred to cheaper community-based schemes, leaving some centres half empty and others having to close beds.
However, the National Treatment Agency said there was no crisis.
BBC home affairs correspondent Danny Shaw said live-in centres with detoxification facilities and counselling are widely thought to be the most effective way of dealing with the most hardened addicts.
Community-based programmes, while up to 20 times cheaper, are considered less effective than residential treatments.
It is thought drug action teams are sending more addicts to community-based schemes in an effort to save money and meet government targets.
At least half of the main providers of residential drug treatment services in England are reporting severe financial problems because not enough addicts are being referred to them.
But National Treatment Agency chief executive Paul Hayes disputed the claims.
He said occupancy figures provided by rehab and detox centres showed bed occupancy, monitored weekly, was at 80% this year compared with 85% last year.
"We would expect to run at 85% or thereabouts. You would expect some empty beds because people drop out, or there are delays in admissions."
He told BBC Radio 4's Today programme that there was a "real problem", but the agency did not think it was as widespread or significant as implied.
"We particularly don't see it as being caused by spending decisions being taken locally in order to spend money on treatments that are less effective but cheaper," he said.
"The spending plans that local drug action teams put in place for this year actually showed a 50% increase in the amount they were planning to spend on residential treatments."
Spending is set to increase from £48m to £72m, bringing residential treatment to 12% from 9% of the treatment spend, he said.
Last month a watchdog said drug users seeking help to quit their habit faced a "postcode lottery" of care.
The Healthcare Commission and the National Treatment Agency for substance misuse reviewed the services provided across England.
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