The number of GP prescriptions rose by a third between 2004/5 and 2011/12 while the cost of these drugs fell by 11%, according to the Audit Scotland report.
It said better prescribing support for GPs and a fall in the cost of some drugs were behind the savings. The NHS could save a further £28m by tackling drug wastage and promoting generic prescribing, Audit Scotland said.
The Scottish GPC welcomed the findings and backed calls for further prescribing support for practices.
GPs in Scotland issue 91m prescriptions a year, costing the NHS nearly £1bn.
Costs had risen by 50% in real terms in the seven years to 2004/5. Since then, the Scottish government and the NHS have tried to improve the quality and cost effectiveness of prescribing.
In response, GP prescriptions rose by a third within seven years due to the ageing population, the introduction of the QOF, a rise in clinical guidelines and new initiatives such as health checks.
Yet during this time, spending on drugs prescribed by GPs fell by £120m. Cheaper statins and better information and feedback on prescribing habits are though to be behind the fall.
Audit Scotland expects primary care to save a further £86m from expired drug patents in 2012 and 2013.
The report found over 900,000 patients aged over 50 are taking four or more different drugs.
Caroline Gardner, auditor general for Scotland, said the NHS had 'significantly improved' how it manages spending on prescription drugs.
'It has achieved this through providing doctors with more support and guidance and using better information about what GPs are prescribing,' she said. 'Demand for prescriptions is likely to increase further and it's important that the NHS continues to work with GPs to make sure patients get the drugs they need and spending is well managed.'
GPC Scotland chairman Dr Alan McDevitt said: 'Prescribing costs in the NHS are second only to workforce costs in the health budget and therefore opportunities to make savings here can have a significant impact on health spending.'
But he said the wider impact of GP prescribing on the NHS should be considered, 'rather than simply seeking to reduce the number of prescriptions issued'.
He warned that widespread generic switching was 'not the answer' for some patients, but supported calls for more pharmacy advisers to support GPs on prescribing.