The latest sick day figures indicate an approximately 56% increase since 2019, when the NHS started categorising sick days by type.
Back then mental health days averaged around 400,000 a month.
The new figures take the total number of mental health-related sick days up to 3.6 million in the first half of this year.
A spokesman for the British Medical Association said: “This is the result of a workforce who have been struggling for years to look after patients in a health system that is under unrelenting, severe pressure.”
The NHS acknowledged that the figures were far too high and that it was doing everything it could to address the issue.
One spokesperson from the health service commented: “The NHS is offering a range of mental health and wellbeing support to help staff stay well and feel supported at work, which should also help bring sickness absence down to more sustainable levels.”
Labour continues to face a raft of challenges relating to the creaking health service.
The NHS waiting list now stands at 7.41 million, despite a £25bn cash injection by the Chancellor.
One in 10 NHS appointments and operations are now being carried out by the private sector in an attempt to address the wait times and more than half a million British patients left the UK for healthcare overseas last year.
This November, NHS doctors are set to strike again. This will be the 13th strike in the long-running pay dispute since March 2023 and is expected to cause significant disruption, particularly in hospitals.