"Legal highs" are causing an increase in violence in UK prisons, it's claimed.
Inspectors, inmates and people working with drug addicts are particularly concerned about the rise in the use of "Spice".
Newsbeat has seen figures which report a seven-fold increase in the number of people seeking help with new psychoactive substances (NPS).
The government said it takes "a zero tolerance approach to drugs in prison".
The new numbers come from RAPt (Rehabilitation for Addicted Prisoners Trust) which works in 26 prisons in England.
In April to September 2014 it saw 87 people asking for help with NPS. That compares to 622 for the same period this year.
Mike Trace, the charity's chief executive, told Newsbeat: "Our frontline teams have seen an alarming surge in the use of new psychoactive substances in just the last year.
"Staff are reporting distressing levels of violence, both from the effects of these drugs but also the lucrative market exploited by gangs."
Newsbeat has also spoken to former prisoners who say Spice is "everywhere".
"It's called green crack, once you have taken it once, you're on it," explained Dave.
"The minute I picked up that legal high I couldn't put it down."
The chief inspector of prisons in England and Wales, Nick Hardwick, said the circulation of these substances is leading to a rise in gang violence.
"People have died and certainly people have been very ill and because there is so much money to be made in the trade of spice.
"It's leading to a big increase in violence. It's a rapidly escalating problem. It's getting worse by the day."
He also told us that he thinks the numbers reported by RAPt are just the "tip of the iceberg".
"Many of the people who are using Spice and do have a problem with it in a prison environment may not be referring themselves."
A report by the Prisons and Probation Ombudsman - which looks at deaths in jails - found new psychoactive substances played a part in at least 19 prisoners fatalities between 2012 and 2014.
The government says it is trying to tackle the issue of NPS in prisons and it is looking to make them illegal.
A Prison Service spokesman told Newsbeat: "There are already a range of robust measures in place across the prison estate to detect drugs, including the use of search dogs and intelligence-led searches.
"We have also introduced tough new laws meaning those who smuggle packages over prison walls, including new psychoactive substances, face up to two years in prison."
One of the difficulties for prison governors is that the chemical make-up of spice is always shifting.
Dr Hazel Torrance, a toxicologist at Glasgow University, told us this means it has become "a moving target".
"The number of different substances is huge and they're all trying to mimic things like cannabis.
"We know very little about these newer ones and every time someone tweaks the structure it's another drug to try and test."
Dr Torrance told us the analysis is basic and the substances are now very dangerous.
"Some tests may be triggered by the legal highs, but when they are sent for confirmation those tests won't include legal highs, so they won't be tested for. It's a major flaw.
"The effects they produce are not the same as cannabis.
"Cannabis is not a drug associated with fatalities but these synthetic cannabinoids have been involved in some."
Mike Trace from RAPt agrees and argues there needs new ways of tackling the issue.
"Increased security and testing are important, but to undermine the prison drug market in the long term, every prison should have a drug recovery wing."
There's more information here if you want to get help or advice about legal highs.