According to the OECD report, which is based on data from the member states, Sweden had 55 opioid-related deaths per million inhabitants in 2016. That is more than doubling compared to 2011, when the corresponding figure was 24 deaths.

The only OECD country that, according to the report, has seen a larger increase is the US, where the increase went from 74 to 131 between the same year.

In addition, Sweden was in fourth place among the world's all OECD countries when it comes to the number of opioid-related deaths per million inhabitants in 2016.

May cause suffocation

Opioids, which are the collective names for both heroin, methadone and substances in painkillers, occur in 95 percent of drug-related deaths in Sweden, according to the Public Health Authority. One reason for the high mortality rate is how they function purely physiologically.

- What happens when you take too much is that you can suffer from respiratory paralysis, that's what makes them so deadly. Even if the dose does not in itself knock out the body functions, you suffocate, says investigator Daniel Svensson.

Determining exactly why mortality is so high in Sweden is not easy. According to Daniel Svensson, there are several possible causes.

Sweden has had a marked increase in opioid-related deaths between 2011 and 2016. Data on the number of deaths in Canada 2011 are lacking in OECD statistics. Photo: SVT Design

New forensic technology

A partial explanation is that new technologies were introduced in forensic investigations in 2011.

- So just these years, the technology has led to finding substances you did not do before, it has helped to identify more of these deaths.

But there is also a real increase, according to Svensson. To some extent, it is about substances called NPS, New Psychoactive Substances, which are chemically similar to existing drugs but which have various minor adjustments.

- These are new drugs that are emerging and are intended to deceive the legislation. They are not drug classed when they show up, so there will be no crime. Then they are classified and then they tend to disappear, then a new one emerges.

Extremely potent and easy to overdose

Due to increasing online sales, the drugs are readily available. In addition, the synthetic opioids are "extremely potent" - and thus easy to overdose.

- There is not much you need to overdose on in terms of quantity to make it life-threatening.

Another contributing cause of the large number of opioid-related deaths is the frequent occurrence of drugs. For example, opioids in various forms are common in pain medicine after an operation and are thus easily obtainable.

"Can misuse completely common medicines"

But unlike the USA, for example, Sweden has no major problem with exaggerated regulations, according to Daniel Svensson. Prescriptions of opioids have even declined in recent years.

- It is possible to misuse completely ordinary medicines. You can use what you have been prescribed in a way that is not intended, to abuse, resell or harm yourself.

And just the latter, that deliberately injuring oneself, is one aspect Daniel Svensson thinks could be lifted more.

"Large element of mental illness"

- About half of the deaths based on our way of counting are linked to suicide or unclear and not accidental overdoses. There is a large element of mental ill-health, loneliness and vulnerability - while also having access to these medicines that can potentially be fatal.

Working against mental illness and being able to identify it, for example, in relation to prescribing medicine, is therefore an important factor in counteracting drug use with a deadly outcome.

- It's as important as a customs issue or a police question.