A report's revealed drugs worth #40,000 were found at a "very unsafe" prison. 350 litres of illicitly-brewed alcohol known as "hooch" was also discovered at HMP Garth over Christmas.
There are 800 adult males at the training prison in Lancashire..
A report on the jail from HM Inspectorate of Prisons said the drug strategy committee at Garth was "much improved".
But it also says: "Despite a coordinated effort to reduce drug supply and demand, very high levels of finds, positive random mandatory drug testing rates and our survey all pointed to a high level of availability of illicit drugs, including new psychoactive substances, diverted medication and illicitly brewed alcohol.
"Almost half the population said that it was easy to get drugs at the prison, and approximately one in five said that they had developed a drug problem while there - both of which were higher than at the time of the previous inspection."
The report described NPS - previously known as legal highs - as "particularly problematic", saying they were linked to medical emergencies and prisoner debt and violence.
The drugs - which mimic the effects of illegal substances including cannabis - have been identified as a major factor behind the deterioration in safety seen across prisons in England and Wales.
Ministers have unveiled a wide-ranging package of measures to reform jails including the introduction of mandatory drugs testing.
HMIP, which visited Garth in January, warned that levels of violence at the jail had increased "substantially" with many incidents linked to drugs, gangs and debt.
Assaults on staff had also risen, while dozens of prisoners were held separately because of fears for their safety.
The watchdog did however find the prison had made real progress in work to rehabilitate prisoners.