The Mayor of London Boris Johnson has called for better awareness of mental health as countries across the globe mark World Mental Health Day.
Mental ill health affects one in four Londoners and costs the capital an estimated £26bn ($41bn, €32bn) each year, according to a report commissioned by the Conservative Party politician.
The research also revealed that around two million Londoners will experience mental ill health in 2014, which can affect every aspect of life, from family relationships, to the ability to work and cope at school or college.
"Mental ill health is an issue that affects millions of Londoners, yet we are too often frightened to discuss it, worried about what people might think, or unaware of who to turn to," said Johnson.
"World Mental Health Day is an opportunity to bolster awareness of this issue amongst businesses, schools, colleges and Londoners in general, to help break down the oppressive social barriers that exist around mental ill health and get people the help and support they urgently need."
The Mayor's Office has identified mental ill health as a "priority issue" and said it is likely to be a key concern in a report published soon by the London Health Commission.
"People are still embarrassed to talk about mental illness, and there is still a culture of blame and shame," said Marjorie Wallace, founder and chief executive of the charity SANE.
"That is why we launched our Black Dog campaign, so that people passing by can see a visible symbol of their inner, darker feelings.
"It's easier to say 'I've had a Black Dog day or week' than it is to say 'I've had anxiety or depression'."