Inspectors found levels of violence of all kinds were far too high at HMP Leeds, where 91 per cent of cells were holding more inmates than they were designed for.
There were four self-inflicted deaths at the prison since it was last inspected in 2015, while another occurred during the latest visit in October and November.
HM Inspectorate of Prisons also found that in a survey, 63 per cent of prisoners said it was easy to get illicit drugs in the establishment.
Publishing the report, Chief Inspector of Prisons Peter Clarke said: "The prison was last inspected in December 2015.
"On that occasion there had been a deterioration in standards, with declines in three of our four healthy prison tests.
"This inspection found a further decline in the area of purposeful activity, and no improvement in the other three tests.
"Perhaps this should come as no surprise given that the prison is one of the most seriously overcrowded in the country."
Mr Clarke added that there were some "cautious grounds for optimism" and noted that, unlike other prisons, HMP Leeds had not "slipped dramatically backwards" in its performance.
He added: "While it had not managed to buck the trends in violence and the prevalence of drugs that have afflicted much of the wider prison estate, neither had it experienced the shockingly high levels of increase seen in many other prisons."
Michael Spurr, chief executive of HM Prison & Probation Service, said: "Levels of violence, self-harm and drug-use at HMP Leeds are too high.
"But decisive action is being taken to tackle the issues.
"A specialist intelligence unit has been set up and the prison is working with the police to target drug suppliers.
"Body-worn cameras are now in place to support staff in reducing violence and we have strengthened incident management and recording systems.
"The governor and staff at Leeds are committed to improving the performance of the prison and will use the recommendations in this report to drive progress over the coming months."
HMP Leeds, in Armley, is a category B prison which held 1,127 men at the time of the inspection.