Nurses put in almost 700,000 extra hours on top of their normal working day in the first half of the current financial year.
Doctors logged in excess of 40,000 additional hours over the same period.
This led to a combined overtime bill of around £17 million. If the trend continues the final total for 2012-13 will be higher than last year.
Winter illnesses have put Scotland's hospitals under particular pressure in recent weeks and staff at all levels are said to have been working late.
Scottish Labour's health spokeswoman Jackie Baillie, who revealed the figures, said: "The longer our doctors and nurses work, the more likely they are to make mistakes. I am concerned health boards are failing to recruit the right number of staff they need.
"What's worse is when you rely on overtime, you end up paying more.
"In the first six months of this year alone, nurses have worked over one million extra hours at a cost of almost £11m – and that's before the annual winter strain takes its toll. This can't make sense financially."
A Scottish Government spokesman said: "Our figures show that, in 2012, nurses worked less than six hours' overtime each at a cost of £122. For the same period medical staff worked four hours' overtime at a cost of £179.
"All territorial health boards across Scotland are seeing an increase in services funding over the next two years and will see a 3.3% funding boost next year to £9.1 billion – that's 1.3% above the rate of inflation. There are more medical professionals working in our NHS than in 2006."