Antidepressants may significantly increase the risk of developing dementia, experts have warned.

A major new study, published in the British Medical Journal, found a “robust link” between the degenerative disease and the medication, even when taken up to 20 years before a diagnosis.

It suggests some patients with long-term exposure to the drugs could face a 30 per cent increased chance of dementia.

Researchers warned there may be 20,000 people currently suffering from dementia as a result of taking the medication, part of a wider group called anticholinergics, which is also prescribed for patients with bladder conditions and Parkinson’s disease.

The Government medicines safety regulator said it was scrutinising the new findings and last night leading medics called on colleagues to consider alternative prescriptions, although they cautioned patients not to abandon the drugs before consulting their doctor.

The antidepressant medications most implicated by the study include Amitriptyline, Dosulepin and Paroxetine.