NHS patients are being prescribed too many drugs with detrimental effects on their health and the loss of millions of pounds from the health budget, the head of Britain's drug safety regulator has said.

The average 80-year-old patient is taking seven or eight drugs but many were not needed, Professor Sir Alasdair Breckenridge, chairman of the Medicines and Healthcare Products Regulatory Agency (MHRA) which licenses drugs for use in the UK, said.

Wastage caused by excessive prescribing was compounded by patients who took too few of the drugs they were given, with further losses to the NHS and additional risks to their health.

Huge savings for the NHS and big gains for public health could be made by tightening controls on the £10bn NHS medicines bill, he added.

Speaking to The Independent, Professor Breckenridge, who has led the MHRA since it was formed in 2003, said an investigation had been launched into concerns about the lack of training of doctors in pharmacology. He called on the pharmaceutical industry, the medical profession and NHS regulators to reduce multiple prescribing and improve patient compliance, responsibility for which was "falling through the slots" between them.

A study of GPs in a healthcare centre who hired a pharmacist to sit in on their consultations and check the prescriptions they wrote revealed the scale of over-prescribing.

"In most instances the pharmacist was able to prune 30 to 40 per cent of the drugs from the prescription, saving the NHS money and improving the patient's health. Some drugs are continued for long periods beyond the point when they are needed. They were justified in the short term but not in the long term. Pharmacists should be able to question prescriptions that doctors write and ask 'Is this really necessary?' We have more powerful drugs with more possible adverse effects than in the past," he said.

Worries about the lack of training for doctors in clinical pharmacology increased the need for pharmacists to monitor GPs. "We are very concerned about this. Training in pharmacology for doctors has been squeezed. We have set up a working party to look at it."

Sir Alasdair, former professor of clinical pharmacology at the University of Liverpool, said his experience in hospital medicine had shown him that what patients told their doctors and what they did were often not the same.

"Adherence is a hobby horse of mine – it is one of the biggest problems we face today. Around 30 per cent of medicines are not taken by patients – either because the prescription is not dispensed or because patients don't take the medicines prescribed, to the detriment of public health and [causing] huge losses to the NHS.

Whose responsibility is it? No one's. It is not a prime concern of the regulator. It is not a prime concern of the industry – once the drug is sold they are happy about that. We as regulators have got to get more interested. But so has the industry, doctors and pharmacists. The message has got to go out to patients, as well, about the importance of taking their drugs."

Professor Breckenridge said too much emphasis was placed on safety in the debate about drugs when it would be better to talk of risks and benefits.

He said he was impressed by recent research showing a low-dose aspirin taken daily cut the risk of a range of cancers by 21 per cent over five years – and by earlier research showing a protective effect against heart attacks and strokes in patients who had already had a heart attack. But he cited his own study in two hospitals in Liverpool published in the British Medical Journal in 2004 which showed 6.5 per cent of admissions were due to adverse reactions to drugs. Internal bleeding caused by low-dose aspirin was one of the two commonest causes (the blood-thinning drug warfarin was the other).

"On the benefit-risk ratio, people have got to realise it is not all on the benefit side. There is no such thing as a free lunch with drugs."

Keep taking the tablets?

67% The rise in the number of drugs prescribed by GPs in England in the decade to 2009, to 886 million items.

17.1 Average number of prescription items dispensed to every man, woman and child in England in 2009, compared with 10.8 in 1999.

£9.64 Average cost of each prescription item, implying an average spend by the NHS of £165 on drugs per person per year.

42.4 The number of prescription items received each year by the over-60s in 2007, nearly 50 per cent more than in 1997 (22.3 items), at an average cost of over £400 per person per year

£8.54bn The cost of all prescriptions dispensed by the NHS in 2009.