The Scottish heroin epidemic started in Edinburgh, the more prosperous of Scotland's two largest cities. This was largely due to the presence of MacFarlan Smith, which was at one point the world's largest producer of pharmaceutical opiates. That initial cohort of heroin users in the 1980s predominantly used drugs that were diverted from the legitimate pharmaceutical supply rather than smuggled from abroad, which led to an unusually rapid increase in the user population and the illicit market.
https://en.wikipedia.org/wiki/MacFarlan_Smith
The majority of overdose deaths in Scotland involved multiple drugs; for reasons that are not entirely clear, Scottish addicts are particularly prone to concurrently use opiates, benzodiazepines and alcohol in an indiscriminate manner. This vastly increases the risk of overdose due to the cumulative and unpredictable respiratory depression induced by multiple drugs.
http://www.sdf.org.uk/934-deaths-from-a-drug-overdose-in-sco...