Not enough is being done to challenge the "over-prescribing" of medicines in Wales, an assembly committee has said.
AMs were concerned at a 46% rise in items prescribed over the last 10 years by primary care providers such as GPs.
The Public Accounts Committee also heard as many as half of hospital admissions could be due to patients taking the wrong drugs or wrong dose.
The Welsh Government said it expected all medics to make sure medicines were "prescribed and dispensed responsibly".
The committee said there was growing demand for prescription drugs, which have been free of charge to all patients in Wales since 2007.
It was concerned at a 46% rise in the number of items dispensed by GPs and other primary care providers over the last 10 years, at a cost of £800m a year - more than a tenth of the Welsh NHS budget.
Committee chairman Nick Ramsay said: "The issue of medicines management is one which is relevant to everybody, from GPs, medical staff in hospitals and pharmacists to patients.
"We all have a responsibility to ensure that medicines are not wasted or dispensed unnecessarily.
"Everyone on the committee has had experiences of relatives, friends or constituents ending up with medicine cabinets full of medicines and the difficulties of getting items taken off repeat prescriptions.
"What we found during this inquiry was a system needing to change and a system not able to maximise its potential."
Recommendations include a call for health boards to develop campaigns to raise the profile of medicines management, and to make more use of pharmacists to advise patients on their drug needs.
A Welsh Government spokesman said: "We welcome this report and will take time to consider its recommendations.
"We expect all health professionals to make sure medicines are prescribed and dispensed responsibly to ensure patient safety and minimise waste."