Women inmates at a Cheshire prison are being put at risk by a lack of support during drug withdrawal and with mental health problems, a top report says.
The report said women coming off drugs did not have enough support
Chief Inspector of Prisons Anne Owers
said more must be done at Styal Prison to ensure vulnerable inmates' safety.
Although there were some improvements, a system to dispense methadone after five drug users' suspected suicides was "inadequate", she said.
Penal reform group the Howard League branded Styal "unsafe for women".
It urged the courts to consider using alternatives to custody.
The methadone programme was set up at the Wilmslow jail after six inmates were believed to have killed themselves in a single year.
All died within their first month in custody and five of them had a serious drug habit.
Ms Owers said an earlier inspection had stressed the urgent need for a proper detoxification regime in Styal's Waite wing in particular.
But the programme was set up "only after the sixth death" and "in great haste", she said.
She said a regime "focused around methadone dispensing" and lacked proper systems to make sure women could access the detoxification programme.
She told BBC News Online: "Clearly it (Styal) has improved safety but nothing was put around it - there was nothing put in support.
"A lot of women were spending up to 19 hours or more in cells and there was nothing for them to do.
"Obviously coming down from drugs that's very important. In terms of things like support and care plans there was an awful lot more to do."
Ms Owers' report also expressed concern about the use of special cells to hold disruptive prisoners, even those who self-harmed.
One woman was subjected to formal punishment after being cut down from trying to hang herself.
She added that more must be done to help women with mental health problems.
Styal was unique in having a psychiatric unit, she said, but "we have to ask whether a prison is or ever can be the right place to treat acute mental illness".
But she praised "supportive and open relationships" between staff and inmates and said progress had been made in resettling prisoners after release.
Education provision had improved and race relations were "among the best" she had seen.
Director General of the Prison Service Phil Wheatley said substantial progress had been made in detoxification provision, suicide and self-harm policies, making Styal a safer place.
A longer term review of mental health needs was under way, he said.
The Howard League for Penal Reform said courts must make greater use of community sentences.
Director Frances Crook said: "Women are not safe in Styal Prison.
"The director general of the Prison Service should make it clear that women should no longer be sent or held there.
"The prison is failing to provide a service to the public, the courts, the women and the victims."
Juliet Lyon, director of the Prison Reform Trust, described the situation as "one of the most shocking examples of institutional failure in a public service".
She said: "Styal is being used as a dumping ground for the mentally ill and drug addicts who have been failed by society."