Health professionals have been advised that patients who are prescribed anti-psychotic drugs are the least likely to pick up their medicine.
Figures provided by the NHS Information Centre for England show that of all the anti-psychotic drugs prescribed by clinicians, only 85.1% of them are picked up by the patient.
This compares with 98.5% of other drugs that are prescribed.
The data, from 145 GP practices and covering the period between 2004 and 2008, shows that the overall collection figure also dropped from 99.6% in 2005 to 98.5% in 2008.
It has been suggested that better recording systems now employed in GP practices could be responsible to some extent for this difference.
Older people were shown to be better at collecting their prescriptions as GP practices with a higher amount of elderly patients had superior redemption rates compared to practices with large amounts of young people.
NHS Information Centre chief executive Tim Straughan said: “A patient may not redeem their prescription for several reasons such as deciding they don’t need the medication or a reluctance to take a drug they have had side effects from previously.
“A patient may have lost their prescription or obtained their medication through another source - such as during a stay in hospital.”