The government is to spend millions more on "talking treatments" for depression and anxiety in England.
At present there are long waits for talking therapies
Health Secretary Alan Johnson said by 2010, £170m a year would be spent - allowing 900,000 more people to be treated using psychological therapies.
These are just as effective as drugs, says the National Institute of Health and Clinical Excellence.
The plan will pay for itself as people return to work and stop needing benefits, an expert said.
As many as six million working age adults suffer from depression or anxiety at any one time, resulting in a estimated 91 million working days being lost every year.
The problem is estimated to cost the economy £12bn a year.
Currently, treatments such as cognitive behavioural therapy (CBT) are in short supply - on average, patients wait 18 months to start treatment.
The new plan aims to reduce that wait to just a fortnight, in line with improvements in outpatient waiting times in other parts of the NHS.
The Department of Health said that all GP surgeries would have access to the treatments as the programme "rolled out" across the country. It is planned to recruit an extra 3,600 therapists.
Currently, approximately £5m is spent on these therapies per year, and the government plans to spend £30m next year, £100m the year after, finally reaching £170m per year from 2010/11.
Mr Johnson said: "More than one in six people suffer from mental health problems at any one time.
"For many people prescribing medication is a successful treatment but we know that psychological therapies work equally well.
"Improving access to psychological therapies will give people with mental health problems a real choice of treatment."
Researchers say that this will effectively cost the government nothing, and is likely to save them money.
Jason Pegler was diagnosed with bipolar disorder at the age of 17.
After eight years in and out of mental health services, he finally started cognitive behavioural therapy.
"It helped me a lot - it helped me re-evaluate my life," he said.
"I made my relationships more positive, and decided that I wanted to work for myself.
"The essential thing is that it has to come from within."
One forecast suggests that, if 900,000 people receive the therapies, there will be 25,000 fewer people on sick pay and benefits.
The number currently claiming incapacity benefit due to mental health problems is now more than one million.
Lord Layard, from the London School of Economics, who worked with the government to develop the scheme, said: "Depression and anxiety lead to huge costs both to the people involved, and to the country in terms of incapacity benefits and sick pay. It costs more in benefits than unemployment."
He said that the total economic cost of one person on incapacity benefit was approximately £750 per month.
He added: "The single biggest factor in terms of human misery in this country is a history of poor mental health - and this should be a priority for government."
Andrew Lansley, the Shadow Health Minister, welcomed the new funds, but said mental health problems were often the result of many factors, such as poor housing and addiction, which required a multi-agency approach.
Angela Greatley, of the Sainsbury Centre for Mental Health, said: "There are millions of people across the country whose quality of life could be improved vastly by timely access to good quality psychological therapy."
Marjorie Wallace, of the charity SANE, said: "CBT and other therapies can transform people's lives and enable those for whom they are effective to see their future as half full rather than half empty.
"We would be concerned, however, if they were seen as a quick fix panacea for everyone.
"It must not be forgotten that there are many people with depression and anxiety who will need far longer term and more intensive treatment and help."
Mr Johnson also gave details of a new £250m access fund to provide extra GP surgeries in deprived areas and extended hours health centres in every part of the country.
A further £100m will be spent on medical innovation, £130m to extend MRSA screening in hospitals, and £140m to tackle C. difficile, which is posing a growing problem in hospitals.