Expanding Synthetic Opioid Threats: Limits of Test Strips and the Rise of Nitazenes and Orphine Analogues
Clonitazene, etonitazene, and bezitramide (an orphine analogue) have been under international control since 1961 and 1969. Since the launch of the UNODC Early Warning Advisory (EWA), 34 nitazenes and 10 orphine analogues have been reported globally. The years highlighted in official reporting indicate when each substance was first identified through the UNODC EWA system, with 2025 data collection still ongoing.
Several of these substances are already listed under Schedule I of the 1961 Single Convention on Narcotic Drugs. Additional nitazenes were reviewed at the 48th WHO Expert Committee on Drug Dependence (ECDD) meeting in October 2025 and recommended for international scheduling, reflecting the growing global concern about their rapid proliferation.
Growing Use of Nitazene Test Strips—With Important Limitations
As nitazenes have become more prevalent in illicit drug markets across Europe, Oceania, and North America, immunoassay-based testing strips have been increasingly adopted as a harm reduction tool. These strips are used both in formal drug-checking services and in community settings to help identify the presence of certain high-risk synthetic opioids.
However, research has identified significant limitations in their effectiveness.
Most commercially available immunoassay strips are designed to detect only a narrow subset of nitazenes, commonly isotonitazene and/or protonitazene. Nitazenes are structurally diverse, and detection of one analogue does not guarantee cross-reactivity with others. As a result, a negative test does not reliably confirm the absence of all nitazene-type opioids.
In particular, “desnitazene” compounds—such as etodesnitazene (etazene)—have frequently gone undetected in laboratory evaluations. Additionally, detection thresholds vary widely between analogues, further limiting the reliability of these strips for comprehensive screening. As new and structurally distinct nitazenes continue to emerge, the likelihood increases that existing strips will fail to identify them.
Another concern involves false positives. Some nitazene test strips have demonstrated cross-reactivity with caffeine at high concentrations. Because caffeine is a common adulterant in heroin, this cross-reactivity can produce misleading positive results when testing street samples.
The Emergence of Orphine Analogues
Complicating the landscape further is the growing appearance of orphine analogues—often referred to simply as “orphines.” These synthetic opioids are structurally distinct from both FYL and nitazenes.
Importantly, orphines are not detected by nitazene test strips or by FYL testing strips, creating a significant blind spot in current harm reduction strategies.
Brorphine, first reported in 2019, was placed under international control in 2022. Since then, 11 orphine analogues have been reported to the UNODC Early Warning Advisory by 14 countries. Notably, nine of these were reported in 2024 and 2025 alone. A new structural category for orphine analogues has now been formally incorporated into the UNODC monitoring framework.
Data from North America indicate increasing detections of orphines in both seized drug samples and fatal overdoses. In particular, N-propionitrile chlorphine (cychlorphine) has been identified with growing frequency. As these compounds circulate more widely in illicit markets, reliance on immunoassay strips alone may leave critical gaps in overdose risk detection.
Balancing Harm Reduction with Realistic Expectations
Immunoassay testing strips have demonstrated value as engagement tools. They can open conversations, increase awareness of contamination risks, and encourage safer behaviors. However, they are not comprehensive diagnostic tools.
Given the variation between national and regional drug markets, recommendations for test strip use should be developed locally and informed by current forensic and toxicology data. Just as importantly, the limitations of these tools must be clearly communicated to prevent a false sense of security.
In an environment where the illicit drug supply is increasingly unpredictable—and where multiple synthetic opioid classes may be present simultaneously—no single testing method can provide complete assurance.
The UNODC Early Warning Advisory remains a critical resource for monitoring emerging substances. Through its data visualizations and search tools, registered users can track newly reported compounds and evolving trends in near real time.
As the synthetic opioid landscape continues to shift, maintaining accurate surveillance and realistic expectations around harm reduction technologies will be essential to protecting public health.
Source: UNODC