Intellectual disability is a lifelong condition that begins before the age of 18 and is characterised by limitations in intellectual functioning (generally indicated by an IQ under 70) and difficulties with one or more life skills. Around 1% of the population has an intellectual disability.

The new study, published in The BMJ, looked at anonymised GP records of 33,016 UK adults with intellectual disabilities between 1999 and 2013. It found that over one-quarter had been prescribed antipsychotic drugs, of whom 71% had no record of severe mental illness.

Antipsychotic drugs are designed to treat severe mental illnesses such as schizophrenia. There is very little evidence that they help to address behavioural problems not due to mental illness in people with intellectual disability. Despite this, the study found that antipsychotics were often prescribed to people with behaviour problems who had no history of severe mental illness. Behaviour problems that might be seen in people with intellectual disability include aggression, self-injury, destruction to property and other behaviours outside social norms.

People with intellectual disability who also had autism or dementia were also more likely to receive an antipsychotic drug, as were older people.

"The number of people with intellectual disabilities who have been prescribed antipsychotics is greatly disproportionate to the number diagnosed with severe mental illness for which they are indicated." explains study author Dr Rory Sheehan (UCL Psychiatry). "People who show problem behaviours, along with older people with intellectual disability or those with co-existing autism or dementia, are significantly more likely to be given an antipsychotic drug, despite this being against clinical guidelines and risking possible harm."

However, the study also found that the rate of prescribing of antipsychotic drugs to people with intellectual disability had fallen gradually but consistently over the past 15 years, indicating that alternative therapies are being utilised and GPs are changing their practice.

Other classes of drugs used to treat mental illness were also prescribed to people with intellectual disability in large numbers. Drugs used to treat anxiety were the most frequently prescribed, followed by the antidepressants (used to treat depression). Like the antipsychotic group, both of these types of drug were given at substantially higher rates than mental disorders were recorded. This suggests that these drugs might also be prescribed inappropriately in some cases. The researchers paid particular attention to investigating the use of antipsychotics due to their risk of serious side-effects.

Side-effects of antipsychotic drugs include sedation, weight gain, metabolic changes that can ultimately lead to diabetes, and movement problems such as restlessness, stiffness and shakiness.

"Side-effects can be managed, but the risks and benefits must be carefully considered before prescribing antipsychotics to people without severe mental illness," says Dr Sheehan. "Research evidence does not support using antipsychotics to manage behaviour problems in people with intellectual disabilities. Many people with intellectual disability and behaviour disturbance have complex needs and other interventions, such as looking at the support people receive and their communication needs, should be prioritised. Antipsychotics, or indeed any medications, should not be prescribed lightly and are no substitute for comprehensive care."

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Materials provided by University College London. Note: Content may be edited for style and length.

Journal Reference:

1. Laura Horsfall et al. Mental illness, challenging behaviour, and psychotropic drug prescribing in people with intellectual disability: UK population based cohort study. The BMJ, September 2015 DOI: 10.1136/bmj.h4326