The number of people needing treatment for "club drugs" such as Ecstasy, ketamine and "meow meow" is creeping upwards.
Overall drug use has declined in England over the past six years, but the number of people needing treatment for club drugs has risen, the National Treatment Agency (NTA) for Substance Misuse said.
Club drugs are those typically used by people in bars and nightclubs or concerts and parties and include Ecstasy, ketamine, methamphetamine, GHB/GBL and mephedrone.
While they cause a treatment problem for a small proportion of people and are unlikely to replace heroin and crack, they can cause serious physical and mental health problems, according to experts.
In a newly-published report, the NTA said club drug users made up 2% of adults in treatment and 10% of young people in specialist services, but the number needing treatment could continue to rise.
The report, Club Drugs: Emerging Trends and Risks, found around one million people were estimated to have used club drugs last year (2011/12). The number of people treated for club drugs was 6,486, up from 4,656 in 2005/06 - with over-18s rising from 3,122 to 4,479 in that period and those under-18 increasing from 1,534 to 2,007.
Club drug users are often successfully treated, the report found - last year 61% of over-18s and 74% of under-18s using the substances left treatment successfully. But experts warned that services must remain vigilant and adaptable as new drugs emerge.
NTA chief executive Paul Hayes said: "It is clear that some club drug users are developing serious health problems and even dependency. While drug use overall is falling, there is an increase in the number of people turning to treatment for club drugs.
"The numbers remain small compared to heroin and crack addiction, but services need to be geared up to meet these emerging needs. For those who do seek treatment, they stand a very good chance of overcoming their problems."
The report found that ecstasy remained the most commonly-treated drug, but mephedrone and ketamine were said to be joining it as popular choices, contributing most to the increase in those being treated for club drugs.