A new study has been published in the Harm Reduction Journal evaluating the effectiveness of nitazene immunoassay test strips. As a provider of drug checking tools, we believe it is vital to engage with new research to ensure our community has the most accurate information available. The paper, “Evaluation of nitazene immunoassay test strips for rapid in-situ detection of nitazene and nitazene analogs in illicit drug samples,” provides some important data, but also contains findings that could be easily misinterpreted without proper context.
This blog post will break down the study’s key findings, address some of its more conclusions, and clarify what this means for people using test strips as a harm reduction tool in the real world.
The Caffeine “False Positive” – A Matter of Interpretation
One of the paper’s headline findings is that the test strips produced false positives when testing seized heroin samples, which they attribute to high concentrations of caffeine, a common cutting agent.
However, a crucial detail is lost in this summary. The researchers themselves note that a “faint line” appeared on these tests. According to the manufacturer’s instructions—and a fundamental rule of interpreting these strips—any line or mark in the test region (T), no matter how faint, must be considered a negative result.
Therefore, calling a faint line a “false positive” is a significant misinterpretation. It is more accurately described as interference that causes the negative-result line to fade. This is an important distinction because it can cause confusion and lead people to discard a substance unnecessarily. While a false positive is far less dangerous than a false negative, correct interpretation is key to building trust in these tools.
While the paper tested strips from the manufacturer BTNX (which Reagent Tests UK does not sell), our own in-house tests on the strips we provide show a similar fading effect from caffeine, but only at very high concentrations, typically above 1mg/mL (1000µg/mL). The researchers found that a true false positive—the complete disappearance of the test line—only occurred with extreme concentrations between 7-10mg/mL.
Do Faint Lines Matter? A Look at Real-World Concentrations
This brings us to the most relevant question: could a high concentration of caffeine mask a dangerous amount of nitazene? Let’s look at the numbers.
If we take the worst-case scenario from the paper, where a true false positive is caused by caffeine at 7mg/mL (7000µg/mL), the test strip is still incredibly sensitive. A strip with a Limit of Detection (LOD) of 3000ng/mL (3µg/mL) could still detect a nitazene analog present at just 0.04% of the total sample weight (3µg nitazene / 7000µg caffeine).
To put that in perspective, the potent nitazene analog etonitazene is roughly 1,500 times the strength of morphine, or about 100 times the strength of heroin. A heroin-equivalent dose of etonitazene would require it to be present at over 0.10% of the total mass. Therefore, a test that can detect nitazenes down to 0.04% is more than capable of identifying a dangerously adulterated sample, even in the event of it being cut with extreme amounts of caffeine.
Using 1mg/mL as a standard testing concentration would allow detection of 0.28% nitazenes in dry mass even for those which are hardest to detect, and 0.05% for easier to detect compounds like N-desethyl etonitazane.
The Real Concern: Undetected “Desnitazenes”
While the caffeine issue has been overstated, the paper raises a far more critical point: the tested strips were unable to detect ‘desnitazene’ analogs. These are compounds like metodesnitazene or etodesnitazene, which lack the “nitro” group from their chemical structure.
The study found that the BTNX strips failed to produce a positive result for these compounds, even at high concentrations. This represents a genuine risk of a false negative. With etodesnitazene possessing a potency of around 70 times that of morphine, its undetected presence in a substance believed to be heroin could easily lead to an overdose.
This is the most significant takeaway for the harm reduction community. We must be vigilant for the appearance of these desnitazene analogs on the market and recognise the current limitations of immunoassay strips in detecting them.
The Golden Rules of Harm Reduction Testing
This research underscores a core principle of drug checking: it can never be used as a guarantee of safety. Instead, testing is a powerful tool to prevent the most dangerous situations from arising, such as encountering a potent synthetic opioid when expecting traditional heroin.
It is just one tool in a much larger harm reduction toolbox. Its use must always be accompanied by other essential practices:
- Start with a small test dose (“start low, go slow”).
- Never use alone.
- Have naloxone on hand and know how to use it.
- Be aware of the limitations of your testing equipment.
Correct test procedure is also non-negotiable. For nitazene strips, this means:
- Dissolve a very small amount of your sample (a tenth of a dose is a good guide) in about 10mL of water.
- Using warm water and a little lemon juice can help ensure everything dissolves.
- Dip the strip into the liquid up to the MAX line for 15 seconds.
- Place the strip on a flat, dry surface and wait 5 minutes.
- Crucially: two lines, even if one is faint, is a negative result. One line is a positive result. No control line means the test is invalid.
- If you get an unclear result, add 10x more water to the sample and test again.
If you get an unclear or positive result:
- Take a photo of the test strip, the liquid tested and the sample
- Contact Reagent Tests UK (testresultquestions@[ this web URL from this page].uk)
- Dilute the liquid so you have 1mL of water for every 1mg of substance you added previously
- Repeat the test procedure and record the results.
- If you still get a positive result it is likely that you actually have nitazenes in the sample. Please contact us to arrange further testing and get a gift card.
Conclusion: A Valuable Tool, If Used Correctly
The recent study provides valuable data for the harm reduction community. However, it is essential that its findings are interpreted correctly. The risk of false positives from caffeine is low if users are properly informed that a faint line is a negative result.
The far greater risk is the inability of current strips to detect ‘desnitazene’ analogs. This highlights the need for ongoing research and continuing to combine different harm reduction tools to ensure all risks are mitigated.
Ultimately, nitazene test strips remain a vital and valuable harm reduction intervention. They empower people to make more informed decisions about their substance use. It is critical that researchers, healthcare providers, and community members all understand how to use and interpret these tests correctly, acknowledging their strengths and their limitations. By doing so, we can maximise their life-saving potential.
