It now tops 15 million a year to fund prescriptions for the heroin substitute.
Prescribing rates rose by 9 per cent in the same period despite the new strategy to get addicts on the road to recovery, instead of being "parked" on methadone.
Conservative justice spokesman John Lamont said it showed the problem was "escalating".
He added: "It is all too evident that we have become over-dependent on methadone as a 'treatment'.
"Scottish Conservatives worked relentlessly to create a new national drugs strategy, based on recovery and leading to abstinence."
The Drug Misuse Statistics report also revealed that a total of 10,325 people entered drug treatment services in 2009-10, with two-thirds of those using heroin.
The average daily spend on drugs for those entering treatment in the past year was 43. Heroin users spent on average 33, while cocaine users spent on average 108 a day.
But the number of cocaine users entering treatment has dropped, from more than 1,200 in 2008-9 to about 750 in 2009-10. The number of crack cocaine users who entered treatment also nearly halved, compared with 2008-9.
A Scottish Government spokesman said: "Our record increased funding for drug treatment services and significant success in dramatically bringing down treatment waiting times is helping more people recover from drug abuse."