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Last July, the latest figures for drug-related deaths in Scotland led to the crisis being called a public health emergency.

The stats showed that a record 1,187 people died of drug misuse in 2018, a 27% increase on the previous year.

The official figures for 2019 will not be released until the summer but experts fear they could be even worse.

Both the Scottish government and the UK government are holding summits in Glasgow this week to look at ways of tackling the crisis.

1. The worst rate in Europe?

The 2018 figures showed that Scotland's drug-related death rate was higher than all other EU countries but it needs to be said that there are recognised issues with under-reporting in some countries.

While it seems likely that the problem in many countries is worse than official figures suggest, Scotland's drug-related death rate - 218 per million of the population - is by far the highest.

It is about four times that of England and Wales, which has a rate of 51 per million, despite a 17% rise in their 2018 figures.

The latest European Drug Report singles out Scotland as a "point of concern".

It says Scotland, with a population of 5.5 million, reports a similar number of overdose deaths as Germany does with a population of 83 million.

The latest estimates are that Scotland has about 60,000 problem drug users, or 1.6% of the adult population.

Scotland has "proportionately way more drug users than the rest of the UK" says Dr Andrew McAuley, a senior research fellow at Glasgow Caledonian University. "That ultimately has an obvious impact on the number of drug-related deaths."

2. The biggest drugs killers

Most drug-related deaths in Scotland are of people who took more than one substance, so-called poly-drug use.

Opiates such as heroin and methadone are implicated in the vast majority of deaths but users are often taking a lethal cocktail of drugs which increasingly includes benzodiazepines such as etizolam - pills which are often dealt as "street valium" or "street blues".

Etizolam contributed to 548 deaths in 2018, more than three-quarters of all "street benzodiazepine" deaths.

Experts says high-risk opioid users typically misuse benzodiazepines to self-medicate or increase the effects of heroin or methadone. They also take benzos to treat symptoms of psychiatric disorders, negative emotional states and withdrawal symptoms.

3. The rise of the benzos

Benzodiazepines act as a sedative - slowing down the body's functions - and are often prescribed by doctors for sleeping troubles and anxiety.

However, the big problem with mixing street benzos with heroin and alcohol is that they have a similar effect on the body, says Dr Saket Priyadarshi of NHS Greater Glasgow and Clyde addiction services. They depress the respiratory system and leave people more at risk of overdose death, he says.

For years diazepam (valium) was the most common benzo and users often got hold of it through "diverted" NHS prescriptions.

One of the biggest changes in the past six years has been the massive increase use of non-prescribed benzodiazepines or "street valium", which can be much stronger than prescribed tablets.

Etizolam first appeared in the figures for 2012 when it was related to one death. Between 2017 and 2018 it rose from 299 to 548 deaths, an 83% increase.

Dr Priyadarshi says street benzos were a huge concern.

He says: "Often people might think they are taking diazepam but it may be other much more potent benzodiazepines such as etizolam. It is particularly dangerous when used in combination with other drugs like heroin and even prescribed methadone."

Dr McAuley, from Glasgow Caledonian University, says: "We see now people taking handfuls of these pills and sometimes they are stronger than they are expecting, or they re-dose more quickly because the effects do not last as long as prescription benzodiazepines."

Cocaine (273), Gabapentin and Pregabalin (367) have also seen a large rise in drug-related deaths.

4. The 'Trainspotting generation' are badly hit

During the 1980s and '90s there was a significant increase in problem drug users in Scotland, which peaked about 20 years ago, according to Dr Priyadarshi.

These people are often called the "Trainspotting" generation, which refers to Irvine Welsh's 1993 novel and the film of the same name about a group of male Edinburgh friends who get into using heroin in the late 1980s.

There is now an ageing population of drug addicts, mainly men, who have been using heroin for decades, Dr Priyadarshi says.

"Biologically they are ageing much faster than their real age and they develop multiple morbidity, particularly around respiratory diseases, liver diseases and blood-borne viruses and this adds a further vulnerability with regards to overdose deaths," he says.

Last year, more than two-thirds of drug-related deaths were aged between 35 and 54.

The number of people aged under 25 fell in 2017 but rose to 64 last year.

5. It's a problem for urban areas

Problematic drug use is highest in areas of deprivation, where people are not getting opportunities in education and employment, according to Elinor Dickie of Public Health Scotland.

Drug use is 17 times higher in Scotland's poorest areas compared to the wealthiest, she said.

Dundee City Council area has the worst rate in Scotland at 0.31 per 1,000 of the population, closely followed by Glasgow (0.30), and Inverclyde (0.25), which includes the towns of Greenock and Port Glasgow.

Edinburgh's rate (0.16) is the same as the average for the whole of Scotland but is still much higher than the UK average.

The three local authorities with the lowest rates of drug-related deaths in mainland Scotland are Aberdeenshire, as well as East Dunbartonshire and East Renfrewshire which border Glasgow but contain the well-off suburbs of Bearsden, Milngavie, Newton Mearns and Giffnock.

Rural areas such as Dumfries and Galloway, Highland and the Scottish Borders have pockets of problem drug users but their overall rate is much lower than the cities.

6. Dundee has developed a drug problem

Dundee overtook Glasgow as having the worst death rate in Scotland in 2017.

Its drug problem has grown massively over the past decade.

For a city of just 148,000 people to have 66 drug-related deaths in a year is startling.

The city has large areas of deprivation and has had problem drug users for a long time, says Dave Barrie, who works for Addaction in Dundee. But in recent years, he says, there has been a "perfect storm" of cheap heroin, cocaine and the market being flooded by the illicit sale of prescription drugs.

Mr Barrie says black market benzos could be the same strength as 10 prescribed tablets, causing opiate users to risk overdose.

The problem seems to have grown across Scotland but areas such as Aberdeen, Inverclyde, East Ayrshire and Renfrewshire have also seen large rises in drug deaths.