England’s prisons lost almost 150,000 working days due to mental ill health last year, up 44% since 2019.
The Prison Officers’ Association said it had “consistently” called on the service to fund specialised on-site mental health support.
National chairman Mark Fairhurst said relying on peer support would “not assist staff who deal with homicides, suicides, self-harm and bullying”.
The MoJ said officers have access to mental health support and it was “investing around £15m to improve their safety”.
A spokesperson added the government was tackling “unacceptable” levels of violence, self-harm and assaults through additional prison places and sentencing reforms “so our jails create better citizens, not better criminals”.