Mental health problems cost the UK economy an estimated £99bn a year as a report describes how the UK is dealing with a "much larger" challenge than previously thought in tackling the issue.
The Thriving at Work report, commissioned by Theresa May, found that mental health costs employers between £33bn and £42bn a year as sufferers are less productive, as well as other factors such as sickness absences and staff turnover.
On top of this, the report says mental health also costs the government an additional £27bn a year, including the costs of benefits and the £3bn annual costs to the NHS.
The economy also suffers from falls in tax revenue as it is estimated as many as 300,000 people - roughly the population of Belfast or Newcastle - lose their jobs every year because of mental health problems.
The authors – Mind chief executive, Paul Farmer, and mental health campaigner and a former HBOS chair, Dennis Stevenson, said it is "perhaps most shocking" that those with long-term mental health condition lose their jobs every year at around double the rate of those without a mental health condition.
The report was set up to inform employers how they can better support the mental health of all people currently in their employ, including those with mental health problems or poor well-being, to help them remain in and thrive through work.
Farmer said in many workplaces, mental health is still "a taboo subject" and that opportunities to prevent or support poor mental health are being missed.
He said: "In many instances employers simply don't understand the crucial role they can play, or know where to go for advice and support. The human cost of failing to address mental health in the workplace is clear.
"Every employer in the UK has a responsibility to support employees with mental health problems and promote the mental well-being of their entire workforce."
Among some of the recommendations for employers in the report include developing awareness among fellow workers, encouraging open conversations and implementing a mental health plan.
Stevenson said: "It's time for every employer to recognise their responsibilities and affect change, so that the UK becomes a world leader in workplace well-being for all staff and in supporting people with mental health problems to thrive at work."
Prime Minister Theresa May previously said the government has made it a priority to "tackle the injustice of mental illness."
May added: "It is only by making this an everyday concern for everyone that we change the way we see mental illness so that striving to improve your mental health, whether at work or at home, is seen as just as positive as improving our physical well-being."
Responding to the report, Liam Butler, VP of Sales for SumTotal EMEA, said: "Despite increased focus and efforts, we are still a long way from regarding or treating mental and physiological health as the same.
"We need to help to reduce the secrecy and stigma surrounding mental health issues, encourage employees to step forward if they are having mental health problems, and make employers reconsider their own attitudes to mental health related illnesses.
"Ultimately, mental health needs to be brought out of the shadows and into the spotlight of the boardroom, so that executives can ensure their employees have access to the resources and support they need."