An "institutionalised regime" of prescribing and administering opioids without medical justification at the Gosport War Memorial Hospital shortened the lives of more than 450 people, an inquiry has found.
An additional 200 patients were "probably" similarly affected between 1989 and 2000, when taking into account missing records, according to a report by the Gosport Independent Panel.
Hospital management, Hampshire Police, the Crown Prosecution Service (CPS), General Medical Council (GMC) and Nursing and Midwifery Council (NMC) "all failed to act in ways that would have better protected patients and relatives", the panel said.
Its report also highlighted failings by healthcare organisations, local politicians and the coronial system.
The Gosport Independent Panel investigation, first launched in 2014, examined more than one million documents.
It revealed "there was a disregard for human life and a culture of shortening lives of a large number of patients" at the Hampshire hospital.
The report added: "There was an institutionalised regime of prescribing and administering 'dangerous doses' of a hazardous combination of medication not clinically indicated or justified, with patients and relatives powerless in their relationship with professional staff."
When relatives complained or raised concerns, they were "consistently let down by those in authority - both individuals and institutions".
The report concludes: "The panel found evidence of opioid use without appropriate clinical indication in 456 patients.
"The panel concludes that, taking into account missing records, there were probably at least another 200 patients similarly affected but whose clinical notes were not found.
"The panel's analysis therefore demonstrates that the lives of over 450 people were shortened as a direct result of the pattern of prescribing and administering opioids that had become the norm at the hospital, and that probably at least another 200 patients were similarly affected."