The study surveyed people in the Ida-Viru County town of Kohtla-Järve who reported injecting drugs.

It found that newer synthetic opioids are being sold under the names of substances users are already aware of, rather than their actual names.

The research, led by Katri Abel-Ollo of the National Institute for Health Development (TAI), compared self-reported drug use with laboratory urine analyses.

"The synthetic opioid market is changing very rapidly. New substances often enter the market unnoticed and are bought and sold under the names of previously known potent synthetic opioids. Users may no longer know which substance they are taking, and this lack of knowledge makes already high-risk drug use even more dangerous," Abel-Ollo said.

Cyclorphine found in half of samples taken

The study involved 350 people who inject drugs in Kohtla-Järve. Of these, 112 provided urine samples and answered questions about drug use over the previous seven days. Some 33.9 percent reported using a synthetic opioid, naming fentanyl, nitazenes and a street substance called "kange" (strong).

Lab results differed. Cyclorphine was found in half of those who reported fentanyl, nitazenes or "kange," and in 22 people overall — nearly one-fifth of those tested. It also appeared in some who reported other substances.

"People generally know the name under which they bought a substance. Laboratory analysis makes it possible to see which substance actually entered the body. Combining these two pieces of information helps us understand how the drug market is really changing," Abel-Ollo said. Cyclorphine belongs to the orphine group of new 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.

New substances also change the risks relating to drug use

Synthetic opioids vary widely in potency. When a new substance enters the market, knowing its composition matters. "If a person uses an amount they are familiar with, but the substance has changed in the meantime, the effect may be much stronger or different than expected. This increases the risk of severe poisoning and overdose," Abel-Ollo said.

The study also measured how long cyclorphine stays detectable. Where it was found, an average of 17.1 hours had passed since use. Where users reported a synthetic opioid but no cyclorphine was detected, an average of 47.6 hours had passed.

Estonia's synthetic opioid market is changing rapidly

Nitazenes began spreading in Estonia in 2019, reflected in fatal poisonings in 2022. In 2025, orphines including cyclorphine and spirochlorphine appeared.

Abel-Ollo said the study identifies market changes before a new substance acquires its own name among users. "A new substance can enter the market very quickly, while the names people use remain the same for a longer period. Laboratory analysis helps make this change visible and makes it possible to adapt harm reduction measures more quickly," she said.

The findings show drug-market monitoring should combine toxicology with self-reported use. "If a new substance is identified early, information about it can be shared through harm reduction services and healthcare, and people can be warned of the potential danger," Abel-Ollo said.

The study in English was originally published in the scientific journal International Journal of Drug Policy here.

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