Statistics from the National Records of Scotland show 706 drug users died in Scotland in 2015, a 15 per cent increase on the previous year.
The figure was more than double the total for 2005, when 336 died drug-related deaths.
The Scottish Government said the increase was due to a legacy of drug misuse dating back decades which was now increasingly affecting older users.
But critics called for a radical overhaul of drug policy.
According to the figures, people over the age of 35 accounted for 73 per cent of the deaths, up from 67 per cent in 2014. The median age at time of death has also risen from 40 to 41 years old.
Public health minister Aileen Campbell said: “These figures show that we have an ageing group of drug users who are experiencing increasingly poor health. This is a legacy of Scotland’s drug misuse which stretches back decades.
“To address this we have funded research to investigate the issues associated with older drug users through the Scottish Drugs Forum. We have also achieved significant reductions in treatment times for those needing treatment for their drug problem.”
Of the 706 deaths, 49 per cent involved heroin and/or morphine, while heroin-substitute methadone was implicated in 36 per cent of deaths.
Cocaine was implicated in 93 deaths; ecstasy-type drugs in 15 deaths; amphetamines in 17 deaths and alcohol in 107 deaths.
Lib Dem health spokesman Alex Cole-Hamilton said: “When will the Scottish Government open its eyes and see that the current strategy is failing drug users, their families and friends? We need a new approach, particularly if we are to reach out to the ageing group of people who have a long history of misuse.”
Scottish Conservative justice spokesman Douglas Ross added: “Behind each of these numbers is a personal tragedy, and we have to do far more to help people beat addiction altogether.”
David Liddell, chief executive of the Scottish Drugs Forum, said the answer lay in getting more users into treatment.
He said: “These deaths are not in themselves inevitable; they are preventable. The evidence is clear. A number of countries have reduced overdose deaths to very small numbers. They have done this through providing effective treatment and care services based on a clear evidence-based vision of what can be achieved and how.”