Study: Drug users may not know which synthetic opioid they are taking
An Estonian study in Kohtla-Järve found that what people who inject drugs believe they took often differs from laboratory findings. Cyclorphine turned up in half of those who named fentanyl, nitazenes or "kange".
A study by Estonia's National Institute for Health Development (TAI) has found that drug users' idea of which synthetic opioid they took often differs from what laboratory tests detect. The research was carried out in Kohtla-Järve, a town in Ida-Viru County, among people who reported injecting drugs. It indicates that newer synthetic opioids are sold under the names of substances users already know, so they may not realise what risk they face.
The study was led by Katri Abel-Ollo of TAI. It covered 350 people who inject drugs, of whom 112 gave urine samples and answered questions about their drug use over the previous seven days. Some 33.9 percent said they had used a synthetic opioid, naming fentanyl, nitazenes and a street substance called "kange" (strong).
What the tests showed
Lab results differed from self-reports. Cyclorphine was found in half of those who named fentanyl, nitazenes or "kange". Overall it was detected in 22 people, nearly one-fifth of those tested, and also in some who reported other substances. Cyclorphine belongs to the orphine group, a new class of synthetic opioids. According to TAI's annual public health report, orphines appeared on Estonia's market in 2025, the same year ten drug deaths were linked to them.
The researchers also measured how long cyclorphine remains detectable. Where it was found, an average of 17.1 hours had passed since use. Where a synthetic opioid was reported but no cyclorphine detected, the average was 47.6 hours.
A fast-changing market
Nitazenes began spreading in Estonia in 2019, which showed up in fatal poisonings in 2022. In 2025, orphines, including cyclorphine and spirochlorphine, appeared.
Abel-Ollo explained that if a person takes an amount they are used to but the substance has changed, the effect may be much stronger or different, raising the risk of severe poisoning and overdose. She said the study makes it possible to spot market changes before a new substance gets its own name among users.
The findings suggest drug-market monitoring should combine toxicology with self-reported use. If a new substance is identified early, information can be shared through harm reduction services and healthcare, and people can be warned. The study was published in the International Journal of Drug Policy.
