In April 2021, the Biden-Harris administration unlocked federal funding to support the purchase and distribution of rapid fentanyl test strips (FTS). Originally developed to detect fentanyl in urine, the technology has been repurposed to identify the ultra-potent synthetic opioid and many of its analogs in liquid preparations of street drugs.

Recent surges in opioid overdoses have been driven predominately by illicitly produced synthetic opioids, including fentanyl and its analogs. Fentanyl is about 50 to 100 times more potent than morphine. Its cousin, carfentanil, has been shown to be 4,000 times as powerful as heroin and 10,000 times stronger than morphine. These ultra-potent synthetic opioids and others that are similar are increasingly present in the illicit drug market, but users rarely know what they’re getting. This lack of transparency makes it difficult to estimate dose or frequency, increasing the risk of accidental overdose.

FTS promise to pull back the veil, returning to users some power over what they put in their bodies. The strips have met with some resistance, but have been widely lauded by harm reduction advocates and the United States’ top public health officials. FTS are not perfect, but they can be an important tool among many in the fight against the nation’s persistent and worsening overdose crisis. Here are five things to know about the portable and easy-to-use kits.

They’re very good at identifying fentanyl and its analogs

Although not developed for drug-checking purposes, FTS actually do this job quite well. A recent evaluation of four commercially available brands found that all detected fentanyl as well as 21 to 24 of the 28 common analogs tested. Better yet, for most analogs they remain accurate at concentrations lower than those prepared for injection, so individuals need not worry about sacrificing too much of their supply to the test. In fact, research indicates that FTS are currently the most sensitive test available, able to detect fentanyl more accurately and at lower limits compared to costlier, more cumbersome point-of-service alternatives.

But… they’re not perfect

While highly sensitive and fairly specific, FTS are not impervious to error.

First, there’s the issue of analogs: Despite exceptional reliability in detecting fentanyl, FTS can miss certain analogs—most troublingly carfentanil—as well as non-fentanyl synthetic opioids. In markets in which synthetic opioids are constantly changing, false negatives could provide users with an unwarranted sense of security, potentially leading them to use a more deadly dose. This risk can be managed via training on interpreting results and encouraging networks to communicate based on their experiences.

The second potential weakness of FTS in the real world is that they are prone to producing false positives for fentanyl when certain stimulants and cutting agents are present in high concentrations. While false positives do not present the same safety concerns as false negatives, they may reduce the utility of the tests. Fortunately, research does suggest that due to the tests’ sensitivity to fentanyl, more dilute mixtures will still pick up on the target drug without producing false positives.

Third, the tests provide limited information. FTS are unable to give users detailed feedback about specific concentrations of fentanyls or the presence of non-fentanyls in their supplies. While this doesn’t hinder their functionality in preventing fentanyl-related overdose, individuals have reported a desire for strips with enhanced drug-checking capacity.

FTS help many who use, but may play different roles for different populations

Despite their limitations, FTS appear to be quite useful and empowering for individuals who purchase and use a range of illicit drugs. However, the specifics will likely look different based on drug market characteristics, drugs-of-choice and more.

Studies from San Francisco to Rhode Island to Greensboro, North Carolina suggest that many individuals change their behaviors in an effort to reduce overdose risk when their drugs test positive on an FTS. This can include starting with a test shot, using a smaller dose, snorting instead of injecting and even discarding the drugs entirely. Some individuals even use the test results to help them avoid drugs associated with less desirable behaviors when they have upcoming obligations, thus minimizing potential social harms.

FTS may be most useful for preventing overdose in communities where fentanyl is on the rise or drug markets are particularly opaque. Even in areas where synthetic opioids are already pervasive and it may be more efficient to assume they are present across the opioid supply, FTS are extremely useful to individuals who prefer stimulants. Individuals who have primarily or exclusively used stimulants—and as such may be opioid naïve—are especially vulnerable to fentanyl in their supply. This population also tends to be less familiar with overdose prevention strategies including FTS, but research indicates they are receptive to using the strips.

Accessing strips and sharing results foster connection

In addition to the direct benefits outlined above, FTS may also serve as a point of connection for those who choose to use them. Key stakeholders—including individuals working in harm reduction, public health and healthcare—in a Baltimore-based study noted that FTS distribution and training provided an opportunity to engage with clients and provide more information about harm reduction, treatment and more. Furthermore, within networks of people who use drugs, FTS and their results are often shared to bolster knowledge about uncertain markets.

Training is key to maximizing their value

One thing some harm reduction advocates worry about with widespread FTS distribution is the potential for user error that could lead to inaccurate results. FTS are indeed straightforward to use, but in order for individuals to get the most out of them, distributing organizations should offer some basic information. Tips should cover storage, timing to run the tests and instructions for preparing the solution—i.e., how to avoid false positives, minimize drug “wasted” and ensure sufficient substance to detect fentanyls. In addition, clients will benefit from discussions about what the strips can and cannot detect as well as how to interpret results in the context of a specific market.

Like many medical and public health interventions, FTS are an imperfect weapon. Nonetheless, they can serve a number of important functions for individuals who use a variety of drugs, across a range of settings. To have the greatest benefit, the technology should be just one tool among many in the fight against opioid overdose.