More than eight million patients have failed to take prescription medicines correctly. Confused by the instructions or unsure about when to take their medication, many are reducing the drugs' effect or putting themselves in danger.

The picture of public confusion emerged as new data from the NHS Information Centre showed that prescriptions have risen by nearly 60 per cent in a decade, to a record 796 million last year. The prescribing bill reached £8.3 billion last year, nearly double the £4.3 billion in 1997. Nearly two thirds of all prescriptions were for people over the age of 60. But a substantial proportion never get used, according to Andy Murdock, director of the Lloydspharmacy chain. “My estimate is that at least £500 million of those medicines are wasted,” he said.

The data emerged from 500,000 medicine use reviews (MURs) conducted by Lloydspharmacy. The reviews were introduced four years ago and are designed to discover whether the drugs are used correctly. “Our pharmacists have reported many instances when patients have been confused by their medicines,” Mr Murdock said.

“One patient set out a range of medicines and described the frequency and dosage for each. It turned out that for several months she had been taking a sleeping pill first thing in the morning.” A man who had been prescribed an asthma inhaler to control his reaction to his cat's hair could not understand why it was not working. He was using the inhaler to spray his cat.

“We know that many patients choose not to complete their course of medication,” Mr Murdock said. “But this study reveals a different type of problem - patients who, for whatever reason, take their medicines incorrectly. The biggest issues are among those who are taking more than one prescription medicine at a time. The problem seems to be more acute among older patients.”

MURs are a free service provided at no charge to the patient. In the half-million so far completed by Lloydspharmacy, 55 per cent resulted in a change of medicine-taking routine, and a further 25 per cent were referred back to their GPs - in many cases resulting in a switch of medication or ending of the treatment.

Prescriptions are rising in part because of efforts to improve treatment of common conditions such as heart disease and diabetes. Yesterday's data from the NHS Information Centre showed that the number of prescriptions written for six areas of health, including the cardiovascular, respiratory and central nervous systems, rose 6.7 per cent between 2006 and last year. In 2006, 561 million prescriptions were written for these areas, rising to 599 million last year. Heart and blood pressure drugs alone accounted for 250 million prescriptions.

Prescriptions of antidepressant medications rose by 9per cent in a year, to 33.8 million last year. Drugs used in diabetes also rose, by nearly 7 per cent to 30.4 million. Prescriptions for genitourinary disorders such as chlamydia and other sexually transmitted infections rose to eight million in 2007.

Meanwhile, the Healthcare Commission says in a new report that the monitoring of controlled drugs such as diamorphine has improved since the murders committed by Harold Shipman.

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