The National Pharmacy Association (NPA) said 'big wins' in NHS savings could only be achieved by changing patient behaviour, rather than persuading GPs to alter clinical practice.
'The NHS should look through the other end of the telescope for the big wins,' said Nanette Kerr, director of pharmacy at the NPA.
'Real value for money can only be achieved if the NHS supports patients to get more benefit from their medicines,' she added.
Up to half of all medicines are not taken as the prescriber intended and adverse drug reactions and poor compliance account for a large proportion of emergency admissions, she said.
'The least cost-effective medicine is one that is used improperly or not used at all once supplied,' she said.
'Prescribed medicines now account for a considerable proportion of the NHS budget and there is no doubt that more value could be extracted from this investment by reducing medicines waste.'
Ms Kerr's comments come in response to a National Prescribing Centre (NPC) document pulling together evidence on key areas where changes to GP prescribing can save the NHS money.
The NPC report, Medicines management options for local implementation argues that reducing use of angiotensin-2 receptor blockers, branded statins and other drugs can save money and improve service quality.