Depression is being over-diagnosed because GPs are too reliant on a “basic” questionnaire designed by a pharmaceutical company which also manufactures psychiatric drugs, campaigners have warned.
The easy-to-use nine-question form sets the threshold for the condition “far too low” and results in patients being wrongly diagnosed and medicated, according an expert at the Council for Evidence-Based Psychiatry.
The PHQ-9 Patient Health Questionnaire was developed by academics funded by Pfizer, which owned the intellectual property and distribution rights. For most of the last 20 years, a chart will have been present in virtually every GP consulting room.
Critics have also warned that a similar tool used for detecting anxiety, also developed by Pfizer-funded research, is similarly setting the bar for diagnosis too low.
They say patients whose symptoms may be the result of unusually stressful or traumatic episodes in their lives are being labelled clinically depressed or anxious because GPs do not have the time to conduct proper psychiatric interviews and rely too heavily on the questionnaires.
But doctors leaders have insisted the charts are used “less and less” and never as a substitute for a full discussion with a patient.
A US-based multinational company, Pfizer manufactures of some of the most commonly prescribed drugs for depression and anxiety in the UK, such as Venlafaxine and Sertraline.
Dr James Davies, researcher at the University of Roehamtpon and co-founder of the Council for Evidence-Based Psychiatry, said: “GPs are very busy and they often don’t have time to do a full interview. “It’s about getting people in and out of the door in 10 minutes. These forms have a very low criteria for anxiety and depression. "Millions of people have filled them and in and got medication, but did they know they were developed by Pfizer?”
The PHQ-9 asks patients questions such as the extent to which they have had poor appetite, low energy, sleep and concentration levels, as well as feelings of low self-worth over the past fortnight.
Each answer, such as “on several days” or “nearly every day”, is awarded a score. The points are then added up and matched against a depression severity scale, ranging from not depressed to severely depressed.
The GAD-7 Generalised Anxiety Disorder Assessment works in a similar way.
Previous research has indicated that generalised criteria can be unreliable in accurately assessing patients’ mental health status, with field trials showing that two psychiatrists will disagree on a diagnosis of major depressive disorder or generalised anxiety disorder in up to 40 per cent of patients.
Brian Dow, Director of External Affairs at the campaign group Rethink Mental Illness, said: “There is no magic formula for diagnosing a mental illness - signs and symptoms in each person can be both varied and sometimes complex to decipher.”
However, Professor Sir Simon Wessely, President of the Royal College of Psychiatrists, said PHQ-9 and GAD-7 are “screening tools, not diagnostic criteria”. "They are used less and less by GPs, and where they are still used, scoring highly does not automatically lead to medication,” he said.
Meanwhile Chair of the Royal College of GP, Professor Helen Stokes-Lampard, defended the skills of family doctors, denying they applied a “one-sized-fits-all approach” to diagnosing mental ill-health.
The Government has promised 3,000 extra mental health therapists to work in GP practices by 2020.
A spokesman for Pfizer said the questionnaires were designed to “support the evaluation and diagnosis of patients”.