Questions have been asked about Scotland's methadone policy after a Perth man admitted taking the substance for 18 years, while still on heroin.
Martin Ramsay, 34, was put on methadone when he was 16 to encourage him to give up heroin.
His situation was revealed when he appeared in court to admit stealing five boxes of perfume.
The Scottish Government said methadone did not work in all cases but had allowed many people to give up heroin.
Sheriff Robert McCreadie, who heard the shoplifting case at Perth Sheriff Court, said: "It seems incredible that he is on a methadone programme and is still taking heroin.
"I am anxious that he is now 34 and has been taking methadone for so long. We are now two decades later after he first took it."
Neil McKeganey, professor of drug misuse research at the University of Glasgow, said: "I think that would be regarded by many people as a rather shocking state of affairs in which an addict may be continuing to use heroin but receiving highly addictive medication on top of that, placing him or herself at a real risk of overdose.
"Clearly if you've got somebody receiving that medication approaching 20 years then it hasn't been a stepping stone to their recovery.
"It's been a state of near constancy over a very long period of time.
"In fact, when someone's been on it that long you've to ask at what point is it ever likely to be raised that they start to come off their methadone and conceivably then they can be on it for another 20 years or even longer in some circumstances."
'Sense of urgency'
Prof McKeganey said it costs about £2,800 to fund methadone provision for one addict for one year, and the programme could be costing about £56m in total each year.
"The cost of the programme is very very large indeed and I think it's quite right to ask, with an increasing sense of urgency, what the benefits of this programme are for individuals especially where they are left on it for as long as this," he said.
A Scottish Government spokesperson said: "Decisions on substitute prescribing are taken by clinicians, taking into account the best interests of the individual.
"Our national drug strategy - unanimously endorsed by parliament - is focused on outcomes.
"Getting people well along the road to recovery is more important than how they get there and it is therefore important that we have a range of treatments available."
Ramsay was placed on probation for 12 months and ordered to carry out 80 hours unpaid work for the theft of the perfume. The sheriff also ordered him to undergo drug counselling.