Staff at a women's prison in Cheshire face a daily battle to keep inmates alive, according to a BBC documentary being shown on Monday night.
Documentary makers were inside Styal Prison for six weeks
HMP Styal, near Wilmslow, was criticised in a report last year after the deaths of six inmates in 12 months.
New governor Steve Hall invited cameras in to the jail to witness the problems faced by his staff on a daily basis.
In the six weeks programme makers were inside, there were about 150 incidents of self-harm or attempted suicide.
Twenty-five women were on regular observation.
"Forty per cent of my population have previously suffered harm before they even arrive in custody," said Mr Hall.
"It's very, very widespread here, so we have processes and systems to try to get people to engage in the reasons for self-harming.
"If it's sexual abuse, we have treatment programmes that help them deal with that and overcome those difficulties.
"If it's drugs we have detox programmes that help them to either come off drugs entirely or stabilise or reduce their drug-taking, so that when they go back into the community they are reliant on legal rather than illegal substances."
Women on the Edge: The truth about Styal Prison will be shown on BBC Two at 2100 GMT.