Almost two-thirds of inmates at Durham Prison said it was easy to to get drugs, inspectors have reported.
Despite a strategy to address drug use at the jail, HM Inspectorate of Prisons found 30% of prisoners had acquired a habit since coming into the facility.
Lack of safety was also an issue, alongside “worryingly high” levels of self-harm and self-inflicted deaths.
A prison and probation service spokesman said progress was being made, but there was still much to do.
HMP Durham became a reception prison in 2017, and about 70% of the 900 inmates are either on remand or subject to recall.
Peter Clarke, chief inspector of prisons, said: “Our overriding concern was around the lack of safety.
“Since the last inspection in 2016, there had been seven self-inflicted deaths… and a further five where it was suspected that illicit drugs might have played a role.”
Although there was a strategy to address the drugs problem, the leadership was “immensely frustrated” by the fact there was no modern technology available to help stem the flow.
It was also reported some promised scanning equipment had been “diverted to another prison”.
Alongside these concerns, inspectors noted “many positive things happening”, including the introduction of in-cell phones and electronic kiosks for prisoners to make applications, which had “undoubtedly been beneficial”.
Michael Spurr, chief executive of Her Majesty’s Prison and Probation Service, said: “Safety is the governor’s top priority and, while Durham has significant challenges, progress is being made.
“We are developing a national strategy to restrict [drug] supply, reduce demand and build recovery.
“We are under no illusions that there is much still to do.”