Depression is being overdiagnosed because GPs are too reliant on a “basic” questionnaire designed by a pharmaceutical company which also manufacturers 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.