The cost of NHS prescriptions increased by £36m in the last year, prompting concerns about how health boards can continue to balance budgets.
New statistics show that £1.18bn was spent on prescriptions in 2011-12, with the vast majority written by GPs.
The number of items prescribed rose to 94.9 million, up 3.8% from 2010-11.
The Royal College of Nursing (RCN) said its analysis found that nine out of 14 health boards overspent on GP prescribing during the financial year 2011-12.
RCN Scotland director Theresa Fyffe said: "This latest increase in prescribing costs, on top of years of growing spend on prescribing, comes at a time when the overall health budget is virtually at a standstill.
"The pressure is mounting on health boards to make increasingly difficult decisions to balance their books while still maintaining quality services that meet growing patient demand.
"That is why we have consistently called for health boards to be more open and honest about what they currently spend their money on and what their plans for the future consist of. Only then will they have a chance of bringing the public, patients and staff with them when they make difficult decisions to change the way health services are provided."
The SNP administration abolished prescription charges in Scotland in April 2011.
The health budget has been protected in Scotland but public spending watchdog Audit Scotland said annual increases in funding must compete with pressures from pay, fuel and drug prescribing, alongside an ageing population.