Strathclyde Chief Constable Campbell Corrigan has revealed the drugs he most worries about.
Not heroin, amphetamines or cocaine: he loses sleep over so-called "legal highs."
"They terrify me, they absolutely terrify me," said the force's most senior officer.
"There are young people who think these are not really drugs at all, but something between those high-energy drinks and cannabis.
"That is absolutely not the case."
Strathclyde Police has issued warning after warning about the substances their officers refer to as "new drugs" than as "legal highs".
They are talking about supposedly lawful products sold in "head shops" – the name given to premises which sell "legal highs", including Glasgow city centre premises – and on the internet as plant food or incense, but clearly intended by consumption.
Such legal highs include Annihilation, a product sometimes sold in packaging featuring a nuclear mushroom cloud, which was flagged up by the force this month after nine people needed hospital treatment after taking it.
Glasgow has been targeted by those pushing such products – which often, in fact, contain toxic substances or illegal Class A drugs, such as escstasy or cocaine.
Mr Corrigan believes the products are transforming a drugs market previously dominated by big illegal products that were taken by older men and women familiar with their habits.
Back in the 1980s and 1990s the evening Times reported many heart-breaking stories about Glasgow mothers mourning the death of their children killed by heroin.
Now deaths are higher than ever – but it is children mourning the death of their parents, who were long-time addicts in their 40s and 50s.
Younger people are not turning to Glasgow's Class A drugs of choice, such as heroin.
Mr Corrigan believes that is because they know more about such substances than any previous generation. But some are taking risks with products they think are legitimate.
He said: "Young people are more clued on the use of what we would term Class A drugs, such as cocaine and heroin, and they are not as likely to experiment and I think that is brilliant.
"Where I think there is a massive risk – having spoken to young people about it – is the notion that these legal highs are not really dangerous. But we are seeing evidence of similar drugs causing multiple deaths across the world.
"Some of these legal highs are a mixture of actual controlled drugs because the people who make this are completely unscrupulous and don't know from one batch to another how much harm is contained in each sachet or pill or batch or whatever.
"What worries me most in the arena of drugs? I would say legal highs – by a mile."
Legal highs are sold in the High Street and online.
Police are looking at what they like to call "audaciously legal" ways of stopping the sales.
It takes considerable time for UK Government regulators to classify such products, by which time they may already have disappeared from the market.
But Mr Corrigan does not want to wait for such moves. He hints at alternative routes to shut down premises that peddle legal highs.
He said: "What would you say to retailers who sell this? Don't. At some point in the future we will get legislation and the Government is rapidly helping us with this.
"Everybody is aware of this and nobody is sitting on their hands."
Mr Corrigan also had a message for anyone thinking about taking a 'new drug'. He said: "Don't just accept my warning about it: read up on it. It's not safe. Full stop."
THE "legal highs" may be marketed as legitimate, but many of them routinely contain the illegal drugs they are supposedly trying to mimic, including cannabis, cocaine and ecstasy.
Marketed as a herbal incense but, in reality, claims to be a kind of fake cannabis. Contains a chemical that is part of a group of drugs known as synthetic cannabinoids. Linked to a number of people who recently required hospital treatment in Glasgow. Sold in a pack with a nuclear mushroom cloud.
Brand name of a "legal" smoking mixture or incense which, like Annihilation, contains synthetic cannabinoid. The UK Government announced this month it was to be banned. Sometimes sold in packs with cannabis leaves or black snakes on them.
Sometimes called "He Man", it tries to mimic the tranquilliser ketamine. Police and doctors warned last week about pink tablets, some with a cherry logo, containing the drug being sold in Glasgow after a young man had an extreme reaction to it this month. Sometimes clubbers and others are told 5-IT is ecstasy.
Marketed as a "research chemical pellet", this "high" contains a synthetic chemical that mimics the effects of stimulants, such as amphetamine and ecstasy. Linked to the death of a 19-year-old reveller at this year's RockNess festival.
MXE or MEXXY
A tranquilLiser similar to 5-IT but now scheduled to be banned after at least two deaths were recorded in England.
Banned last year, this drug, also called Mephedrone, was one of the first legal highs to come to public attention. Users get heart palpitations and blurred vision and other serious symptoms.