Almost one in ten people over the age of 15 are on anti-depressants, official NHS figures showed today.

And Scotland spends more than £40 million every year on anti-depressants, despite a fall in last year's costs.

It prompted opposition claims that Scotland may be turning into a "Prozac nation".

The number of anti-depressants prescribed has more than tripled in the last 15 years, according to NHS Scotland statistics on medicines used in mental health.

It has grown from 1.16 million items to 3.83 million between 1992/93 and 2007/08.

It is also estimated that 9.3% of the Scottish population aged 15 and over use an anti-depressant drug every day.

"The high numbers of Scots making daily use of anti-depressants is cause for serious concern," said Lib Dem public health spokesman Jamie Stone today.

"The health secretary must ensure that in Scotland anti-depressants are not allowed to become a quick fix for depression.

"I hope that these figures prompt health professionals to look at viable alternatives to anti-depressants.

"We should be trying to help people through the rough periods in their lives without relying on tablets.

"We must not allow Scotland to turn into a Prozac nation."

The gross ingredient cost of anti-depressant medicines in 2007/08 was £40.4 million, down from £43.7 million in the previous financial year. The decrease is ascribed to a number drugs being reduced in price.

The prescription of the two main types of anti-depressant drugs - the older tricylics and the newer "selective serotonin re-uptake inhibitors" - increased by 1.6% and 5.6% respectively from 2006/07 to 2007/08.

"Monoamine oxidase inhibitor" prescriptions fell by 6.5%, while the prescribing of other antidepressants increased by 8.8%.

The prescribing of drugs for attention deficit hyperactivity disorder (ADHD) grew by 12.3% between 2006/07 and 2007/08, up from 59,461 to 66,756.

The costs of drugs and stimulants used for ADHD increased from £2.5 million to £2.88 million.

GPs issue the vast majority of prescriptions for medicines used in mental health. They include prescriptions written in hospitals that are dispensed in the community but not drugs dispensed at hospitals.

Public health minister Shona Robison said the Government has set a target to reduce the growth in prescribing anti-depressants to zero by 2010 and is investing in alternatives to drugs.

Psychologists and mental health staff numbers have gone up 11% in the past year, she said, adding this will result in improved access to "talking therapies" in NHS Scotland.

"At the same time, it is important to remember that many of these medications have enabled patients who previously would have been disabled by their mental health condition to return to normal and high quality life in the community," Ms Robison added.

Tory health spokeswoman Mary Scanlon said: "This worrying news comes at the back of unacceptably high waiting times for cognitive behavioural therapy, psychiatric and psychological care in many parts of Scotland.

"Patients in the Highlands have had to wait up to 4 years and 7 months to see a psychologist.

"If the Government is serious about reducing anti-depressants, it will need to put more talking therapies in place to ensure that people can be supported to understand and cope with their condition and to assist in getting people back to work."