Scotland could find itself facing a drugs Doomsday that would see primary school children following their parents into drug use, an expert has warned.
Prof Neil McKeganey of Glasgow University said a massive refocusing of priorities was needed to stop the problem spiralling out of control.
Prof McKeganey called for addicts to be properly rehabilitated instead of simply being given methadone.
The Scottish Government is to launch a new drugs strategy on Thursday.
Speaking to BBC Scotland, Prof McKeganey, of the Centre for Drug Misuse Research, said the drug problem in Scotland was twice as bad as in England.
He claimed Scotland had one of the worst drugs records in Europe, but did not do nearly enough wean addicts off heroin, or to prevent people taking up the drug in the first place.
The professor said: "We should have a massive effort on drug prevention because Scotland cannot cope with the drug problem at its current scale.
"If in the next 10 years we saw anything like the growth of Scotland's drug problem we've seen in the last 10 years then you would see public injecting, you'd see cases of drug-related deaths on the streets in Glasgow.
"You'd see increasing numbers of children being brought up in homes where there is no structure whatsoever and those children, because they're living with drug-addicted parents, will start to use drugs possibly even at primary school age.
"The image of where this problem could go is just unimaginable. We cannot afford, in this small country, to allow this drug problem to flourish to anywhere near the degree it has over the last few years."
Prof McKeganey questioned whether the £431m spent on attempting to tackle addiction in Scotland was being used in the right areas.
He added: "I think far too much is being absorbed by the methadone programme.
"I think we need to refocus where that money is spent. We need to massively increase the availability of residential rehabilitation... at the moment our treatment centres are log-jammed."
Describing a recent visit to a recovery community in Italy that is home to 1,800 heroin addicts, Prof McKeganey said Scotland should learn from how other countries were tackling addiction.
"From day one they're involved in productive work and that community is self-funding. They sell the products of what the addicts do," he explained.
"Many people would think a community of 1,800 addicts is hell on earth but they organised the 2005 European show jumping championship. It shows what a community, focussed in the right way, can do."
The Scottish Government is to unveil a five-year plan to tackle drug addiction at Holyrood on Thursday morning.
Prof McKeganey, who has advised the UK Home Office, the World Health Organisation and the United States Department of Justice on drugs policy, said he expected the plan to be a step in the right direction.
But he warned: "I think it's too early to say if it'll make a dent in the problem. I don't know whether the new drug strategy will reduce the number of addicts on methadone.
"If it doesn't then I think many people will say it's failed to achieve what it ought to have achieved."
There are estimated to be about 51,000 heroin users in Scotland, about 21,000 of whom are thought to be using methadone to help with their addiction.