Campaigners say the scale at which these “chemical cosh” drugs are being used pose troubling questions about the quality of life for thousands of people with intellectual disabilities living in institutions or other settings.

A mounting body of evidence shows behavioural interventions and one-on-one support are the most effective way of tackling disruptive or challenging behaviours.

Psychologists who have worked inside the system say a culture of using drugs to control behaviour is an increasingly discredited approach which does not address underlying problems.

The figures on antipsychotic drug use are contained in a supplement to the Irish Longitudinal Study on Ageing, based on a national representative sample of people with an intellectual disability aged 40 and older.

Drug use was highest among those living in residential or institutional settings (54 per cent), followed by community group homes (42 per cent) and independent settings (16 per cent). The equivalent figure for antipsychotic drug use in the wider community is estimated to be between 1 and 2 per cent

Behaviour

Most antipsychotics are approved only for treating major mental health problems, such as schizophrenia. But many doctors use them on an “off label” basis to manage challenging behaviour because of their tranquillising side effects.

Inclusion Ireland, the umbrella group for people with intellectual disabilities, says stricter rules on prescribing are needed to protect vulnerable residents. “They’re [antipsychotic use] driven by the needs of staff or timetables, but not in the best interests of people. This is a serious issue, it’s a human rights issue, but it’s not being taken seriously enough by authorities,” said Paddy Connolly, head of Inclusion Ireland.

In a statement, the Health Service Executive said drugs should not be used as a restraint or to subdue patients, or administered for reasons other than medical necessity.