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A potent synthetic opioid was found in the heroin that caused overdoses, but what are nitazenes?

Fifty-seven people have overdosed in Dublin city since last Thursday.

LAST UPDATE | 15 Nov 2023

TRACES OF A powerful synthetic opioid have been detected in heroin samples related to overdoses in Dublin city in recent days.

Fifty-seven people have overdosed in the city centre area since last Thursday, the HSE confirmed yesterday. No deaths have been reported.

The majority of overdoses happened from Thursday to Sunday, with the number declining since the weekend.

A trace amount of a nitazene-type substance was identified in a brown powder analysed by Forensic Science Ireland last week, prompting the HSE to issue a warning.

But what exactly are nitazenes?

Nitazenes is the name given to a group of potent synthetic opioids including isotonitazene, metonitazene, etonitazene and protonitazene.

They were first developed in the 1950s by researchers who wanted to find an alternative to morphine. Due to their potency and risk of overdose, they were never licensed for medical use.

They have been linked to thousands of deaths in the US and, more recently, a number of deaths in the UK and Northern Ireland.

The HSE has warned that it is “very easy to take too much too soon with synthetic opioids, leading to a drug emergency (an overdose)”.

Nitazenes are relatively new to the European market but are becoming more commonly available.

They can come in pill or powder form, and are often sold under the guise of other drugs such as counterfeit oxycodone tablets or heroin.

The effects of nitazenes are similar to other synthetic opioids but they have greater potency and higher risks.

The symptoms include sedation, pain relief, euphoria, confusion, drowsiness, memory loss, constipation, nausea or vomiting, slowed breathing, and a high risk of overdose.


Tony Duffin, CEO of the Ana Liffey Drug Project, said the number of overdoses in recent days was “unprecedented” over such a short time period.

“It was an unprecedented level of overdose. I’d never experienced that before and I’ve worked for the Ana Liffey Project for 18 years.”

A nitazene-like substance was found in heroin related to at least two of the overdoses in Dublin, but it may have been a factor in more.

Duffin explained: “It was certainly found to be implicated in two samples that they found out of the 57. But that doesn’t mean that they were able to get samples for all 57 people, so it may well be implicated in other overdoses.”

Thankfully no deaths were reported in the last few days but Duffin said “non-fatal overdoses are still very, very serious and very, very damaging to people’s health”.

European issue

There have been growing concerns in recent months about a possible increase in the use of opioids such as nitazenes and fentanyl.

Tens of thousands of people in the US have died from fentanyl overdoses, but the drug is less commonly used in Europe.

The Journal recently reported that the HSE, gardaí and other organisations are working behind the scenes in preparation for the use of synthetic opioids becoming more prevalent in Ireland.

A heroin shortage is expected across Europe following a ban on poppy cultivation by the Taliban in Afghanistan. The vast majority of heroin consumed in Europe – about 95% – comes from Afghanistan.

Eamon Keenan, the HSE’s National Clinical Lead on Addiction Services, said the Irish drug market is generally more influenced by what is happening in Europe than the US.

“Our drug market tends to be dictated by what’s going on in Europe rather than what’s going on in the United States where fentanyl is a big issue,” Keenan told The Journal.

As such, nitazenes are more likely to become a bigger issue in Ireland.

“If we are going to get synthetic opioids, we might be more likely to get the nitazene drugs, which are a different type of synthetic opioids, which have been seen in European countries and in the UK.

“There’s been a number of deaths associated with them in London in the last few months so that might be a concern and we’re keeping a very close eye on that.”

Keenan said that while “a lot of people are talking about fentanyl”, he hasn’t seen any evidence of it here.

“I think the nitazenes in Europe seem to be more of a problem than fentanyl,” he added.

Earlier this year the European Monitoring Centre for Drugs and Drug Addiction (EMCDDA) noted that while heroin remains Europe’s most commonly used illicit opioid, “there is also growing concern about the use of synthetic opioids in some areas”.

A report stated: “Many synthetic opioids are highly potent and pose a risk of poisoning and death.

Only small quantities are needed to produce thousands of doses, making them a potentially more lucrative substance for organised crime groups.

The EMCDDA report noted that since 2009 a total of 74 new uncontrolled synthetic opioids have appeared on the European drug market.

In recent years, most of the newly identified opioid substances reported to the EU Early Warning System have been highly potent benzimidazole (nitazene) opioids.

“Compared with North America, new synthetic opioids (e.g. fentanyl derivatives and nitazenes) currently play a relatively small role in Europe’s drug market overall, although they are a significant problem in some countries,” the report noted.

In February the British Home Office announced that additional nitazene drugs would be made Class A substances.

Their possession is now illegal in the UK and anyone who supplies the drugs will face up to life in prison, an unlimited fine or both.

A number of nitazenes including isotonitazene, clonitazene and etonitazene are listed as Schedule 1 controlled drugs under the Misuse of Drugs Acts in Ireland.

Irish regulations divide controlled drugs into five schedules according to their potential for abuse and their therapeutic usefulness. Schedule 1 controlled drugs have the most restrictions imposed due to their strong potential for abuse and little, if any, therapeutic value.

A spokesperson for the Department of Health said that if other nitazenes emerge and “the necessary risk assessments and evaluations indicate that the substance poses a threat to public health and should be subjected to international control measures, then it will be subjected to such measures in Ireland”.


The HSE has warned that it is obviously safer to not take heroin but if anyone is taking the drug, they should not do it alone, have Naloxone on hand, and take a test dose rather than a regular dose given the high potency of this particular patch.

“Go to your service provider and get Naloxone, that’s a big one. Maybe take a test dose before you take your regular dose. And don’t use it alone,” Keenan advised.

“If you’re with someone who overdoses, contact the emergency services and stay with them until the emergency services arrive,” he added.

Naloxone, a medication which temporarily reverses the effects of opioids, was administered in many if not all of the overdose cases in the last week, homelessness and addiction support workers told The Journal.

The medication is carried by many drug users and is stocked by charities working in the homelessness and drug sectors.

So far this year, the HSE has distributed 3,849 units of Naloxone and trained around 1,030 people in administering it. 

The HSE said it is continuing to collaborate with various partners including Emergency Departments, Dublin Fire Brigade, NGO service providers, An Garda Síochána, and laboratories at the National Drug Treatment Centre and Forensic Science Ireland to “closely monitor the situation”.

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