Unused prescription medicines cost the NHS at least £300 million a year, figures show.

Around half the waste associated with drugs that are prescribed but never taken by the patient is preventable, according to a study commissioned by the Department of Health.

The report found the gross annual cost of NHS primary care waste and that occurring in care homes is £300 million in England, but this could be an underestimate.

“This sum represents approximately £1 in every £25 spent on primary care and community pharmaceutical and allied products use, and 0.3% of total NHS outlays,” the study said.

“It includes an estimated £90 million worth of unused prescription medicines that are retained in individuals’ homes at any one time, £110 million returned to community pharmacies over the course of a year, and £50 million worth of NHS supplied medicines that are disposed of unused by care homes.”

Reasons behind discarded medicines include over-ordering on prescriptions, patients getting better before all the medicine is taken, people suffering unwanted side-effects and the patient dying.

Some of the waste is therefore “inevitable”, the report said.

However, encouraging people to adhere to their prescription regime and overall better management of medicines could lead to even bigger savings, in part because people would suffer less ill health and need less NHS care.

Up to £500 million could be saved in just five areas - asthma, diabetes, high blood pressure, vascular disease and schizophrenia - if medicines were taken in the most optimal manner, according to researchers from the York Health Economics Consortium and the School of Pharmacy at the University of London.

The NHS is also no worse than other countries when it comes to wasting medicines, said the study, which was based on figures for 2009.

Report co-author, Professor Paul Trueman, said: “Many health professionals and members of the public believe that the physical waste of NHS medicines is a major issue. We should do everything we can cost effectively to reduce it. But we have not found that the NHS has a systemic problem with drug wastage which marks it out from other health services.

“In value terms there is more to be gained from helping people to take their medicines more effectively, even though this may increase the overall volume of drugs paid for.”