VIENNA - The Taliban-ordered crash in opium production in Afghanistan, long the world's dominant supplier, could drive up overdose deaths as heroin users switch to synthetic opioids already proving deadly in Europe, a UN report said on Wednesday.

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The cultivation of opium, from which heroin is made, fell by 95 percent in Afghanistan last year after the Taliban banned the production of narcotics in 2022. Globally, opium production fell by 75 percent, the United Nations Office on Drugs and Crime said in its annual World Drug Report published on Wednesday.

Overdose deaths from nitazenes, a type of synthetic opioid more potent than fentanyl, have been reported in Ireland, Britain, Estonia and Latvia, UNODC research chief Angela Me told reporters

"The result of a prolonged shortage of Afghan opiates could have multiple consequences in Afghanistan and countries of transit and destination for Afghan opiates. The purity of heroin on the market is expected to decline," the UNODC said.

READ MORE: UN: Afghanistan poppy supply plunged 95% after Taliban ban

Preliminary field observations indicate a possible slight increase in Afghan opium cultivation this year but it is unlikely to return to pre-ban levels, the UNODC said.

While there were "no real shortages" in the main destination markets for Afghan opiates such as Europe, the Middle East and South Asia were reported until early 2024, that could change if future harvests remain small, it added.

"Demand for opiate treatment services, including for methadone, buprenorphine, and slow-release morphine treatment, may rise, but if these services are insufficient, heroin users may switch to other opioids," the report said, outlining the potential impact of reduced opiate supply.

"Such a switch may pose significant risks to health and lead to an increase in overdoses, especially if the alternative opioids include highly potent substances such as some fentanyl analogues or nitazenes that have already emerged in some European countries in recent years," it added.

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Overdose deaths from nitazenes, a type of synthetic opioid more potent than fentanyl, have been reported in Ireland, Britain, Estonia and Latvia, UNODC research chief Angela Me told reporters.

Typically a heroin user will buy what they think is heroin but it will have been cut with far cheaper and more potent nitazenes, Me said. The drug is then detected when tests are performed after the overdose death.

The sprawling report also said cocaine supply hit a record high in 2022, the latest year for which data is available. While consumption in the United States appeared to fall, wastewater tests showed consumption increasing in Europe.