The majority of people taking antidepressants may not actually have depression, a new study claims. Researchers discovered more than two-thirds (69 per cent) of people taking antidepressants did not meet the criteria for major depressive disorder, which is also known as clinical depression. Antidepressants are also prescribed for other psychiatric disorders. But the researchers found 38 per cent of those taking the drugs did not meet the criteria for obsessive compulsive disorder, panic disorder, social phobia or generalised anxiety disorder either. Scroll down for video . More than two thirds of people taking antidepressants did not meet the criteria for clinical depression . The U.S. investigators looked at those taking selective serotonin reuptake inhibitors (SSRI), the most commonly prescribed type of anti-depressant. SSRIs are usually the first choice medication for depression and other psychiatric conditions because they generally have fewer side effects than most other types of antidepressant. Writing in the report,  published in the Journal of Clinical Psychiatry, the researchers concluded: ‘Many individuals prescribed antidepressants may not have met the criteria for mental disorders. ‘Our data indicates that antidepressants are commonly used in the absence of clear evidence-based indications.’ Commenting on the study, Dr Howard Forman, medical director of the Addiction Consultation Service at Montefiore Medical Center, said clinical depression is distinct from temporary feelings of sadness. He told Medical Daily: 'We all experience periods of stress, periods of sadness, and periods of self-doubt. 'These don’t make us mentally ill, they define us as human.' In the U.S., official guidelines say clinical depression should be diagnosed if a person has five or more depressive symptoms over a two week period, most of the day, nearly every day. The symptoms include a depressed mood; a loss of interested or pleasure in activities; weight loss, weight gain or changes in appetite; insomnia or increased desire to sleep. In the U.S., official guidelines say clinical depression should be diagnosed if a person has five or more depressive symptoms over a two week period, most of the day, nearly every day. The symptoms include a depressed mood; a loss of interest or pleasure in activities; weight loss, weight gain or changes in appetite; insomnia or increased desire to sleep. Other symptoms include restlessness or slowed behaviour; fatigue or loss of energy; feelings of worthlessness or excessive guilt; difficulty making decisions or trouble concentrating, and thoughts of death or suicide. Other symptoms included restlessness or slowed behaviour; fatigue or loss of energy; feelings of worthlessness or excessive guilt; difficulty making decisions or trouble concentrating, and thoughts of death or suicide. Prescriptions for anti-depressants have more than trebled since 1998 in the world’s richest countries, a study by the Organisation for Economic Co-operation and Development found. The research noted a particular rise in in the use of SSRIs like Prozac and Seroxat. The OECD figures showed Iceland to have the highest prescribing rate, at 106 doses a day for every 1,000 inhabitants in 2011, up from 71 a decade earlier. Behind Iceland is Australia, then Canada, Denmark, Sweden and Portugal. The lowest levels were seen in Chile and South Korea. Separate data from the US shows 11 per cent of Americans over 12-years-old use anti-depressants. As part of the new study, doctors used data from the Baltimore Epidemiologic Catchment Area (ECA) Study Wave 1, which began in 1981, up to Wave 4, which ended in 2005. In total, they used data on 1,071 participants, carrying out four interviews and assessing the use of antidepressants. They found 13 per cent of people in the group reported using antidepressants. The study found 38 per cent of SSRI users did not meet the criteria for obsessive compulsive disorder, panic disorder, social phobia or generalized anxiety disorder or clinical depression (file photo) It's thought that SSRIs work by increasing the levels of a chemical called serotonin in the brain. Serotonin is a neurotransmitter (a messenger chemical that carries signals between nerve cells in the brain). It's thought to have a good influence on mood, emotion and sleep. After carrying a message, serotonin is usually reabsorbed by the nerve cells (known as 'reuptake'). SSRIs work by blocking ('inhibiting') reuptake, meaning more serotonin is available to pass further messages between nearby nerve cells. The NHS Choices website while it would be too simplistic to say that depression and related mental health conditions are caused by low serotonin levels, a rise in serotonin levels can improve symptoms and make people more responsive to other types of treatment. Source: NHS Choices . They then assessed whether the people in this group met the criteria for a mental disorder, as laid out in the latest edition of the Diagnostic and Statistical Manual of Mental Disorders, the U.S. bible for psychiatric conditions. They found that 38 per cent of SSRI users did not meet the criteria for a mental disorder, and 69 per cent did not meet the criteria for major depressive disorder. The news comes after a study found women who take antidepressants during pregnancy are more likely to have a baby with autism. The U.S. study supports previous research which has shown that taking SSRI antidepressants during pregnancy increases a woman’s risk of having a child with the developmental disability. And other American research revealed young adults taking high-dose antidepressants such as Prozac and Seroxat have double the risk of suicidal behaviour. Researchers pointed to previous studies, which found antidepressant drugs are linked with an increased risk of suicidal behaviour and thoughts in children and adolescents, particularly in the early stages of treatment.
Study analysed those taking selective serotonin reuptake inhibitors (SSRIs)
Found 69% did not meet the criteria for clinical depression.
And 38% did not meet the criteria for other mental conditions like anxiety.
Experts: 'Drugs are prescribed without an evidence-based diagnosis'