How testing works

At a glance

Many services combine methods: an FTIR to see the main ingredients, test strips for fentanyl, and a lab for anything unclear. When you search the atlas, each listing says which methods it offers.

Test strips

Test strips (sometimes called immunoassay strips) carry antibodies that react to one drug or family of drugs.

Fentanyl test strips are the most common: small paper strips that react to fentanyl and many drugs like it. You dissolve a little of the sample in water, dip the strip and read the lines. One line usually means fentanyl was found; two lines usually means it was not. Check the instructions on your pack, as brands differ.

• They can’t tell you how much fentanyl is there.
• They may miss some fentanyl-like drugs, and they don’t detect other strong opioids like nitazenes.
• Some drugs, like methamphetamine or MDMA, can give a false positive if the water mix is too strong. The pack says how much water to use.
• Fentanyl is often spread unevenly, especially in pills. Testing one corner may miss it. Crush and mix if you can, or test from more than one part.

Xylazine, medetomidine, benzo and nitazene strips work the same way, one kind of strip for each. Ask your service which ones they have.

• Nitazene strips: a negative result doesn’t rule nitazenes out. When an Ontario drug checking network compared nitazene strips with mass spectrometry on samples from 2025, one brand (BTNX) agreed about 72% of the time and another (Trimedic) about 33%.
• Medetomidine strips are new, and how well they work varies by brand and even by batch. Some batches have reacted to other substances, or to only one form of the drug.
• Benzo and nitazene strips may miss some of the newer drugs in those families, and a benzo strip can’t tell you which benzo is there.

Other strips on a listing are any other kind the service uses, such as ketamine or LSD strips. The listing says which when the service has told us.

Reagent tests

A drop of a chemical (Marquis, Mecke, Mandelin, Ehrlich, Simon’s and others) on a tiny amount of the sample changes colour. The colour points to a family of drugs. Using two or three reagents together tells you more.

• Good for checking that a drug is in the family you expect, and for spotting some common substitutes.
• Mixtures are hard to read, and small amounts, like fentanyl in a cut, usually don’t show.
• They can’t tell you how much is there, and they can’t identify most new drugs.
• They are not a reliable way to check for opioids such as fentanyl. Use fentanyl test strips for that.

FTIR (infrared spectroscopy)

An FTIR machine shines infrared light on a few grains of the sample and compares the result with a library of known substances. A trained tester reads it with you, usually within 10 to 20 minutes.

• Good at the main ingredients. Unlike most lab tests, it also shows the cut: inactive fillers like mannitol, lactose and other sugars, baking soda and salt.
• Can miss anything present in a small amount (often anything under a few percent). That is why services pair it with fentanyl strips.
• Results depend a lot on the person reading them. Matching a mixture against the library takes training and judgement, and an inexperienced tester can miss a drug or name one that isn’t there. It’s fair to ask how sure they are, and whether an unclear result can go to a lab to confirm.
• Some services can give a rough idea of strength for some drugs, but it is not a measurement.

Raman spectroscopy

A Raman device uses a laser and works a lot like FTIR. Handheld models can sometimes test through a clear bag. Coloured or fluorescent samples are hard to read, and like FTIR it can miss things present in small amounts.

Paper spray mass spectrometry

A newer instrument that some services in Canada and Australia run on site. No drug checking service in the US is known to use it yet. A tiny amount of the sample goes on a paper tip and into a mass spectrometer. It is very sensitive, so it can find traces of strong drugs like fentanyl, nitazenes or xylazine that FTIR misses, and it can estimate how much of some drugs is there.

GC-MS (gas chromatography–mass spectrometry)

The standard lab test. The sample is separated into its parts and each drug is identified, including drugs present in small amounts.

• Usually done at a lab, so results take days to weeks. Mail-in services use it. In the US only a handful of labs do this work for drug checking services, and most take samples only through a partner service.
• It looks for drugs, not the cut. Lab results usually don’t list inactive fillers like mannitol, lactose and other sugars, baking soda or salt. FTIR is better for those.
• How much is in it? A lab can only tell you for a drug it measures, and only when there is enough of the sample to weigh first. Most labs measure a short list of common drugs. For anything else they can say it is there, but not how much, though some labs will measure another drug if you ask.
• Some drugs break down when heated and are better tested with LC-MS.

LC-MS and HPLC (liquid chromatography)

HPLC separates a sample in liquid and is widely used to measure how much of a drug, like MDMA, cocaine or ketamine, is in a sample. LC-MS adds a mass spectrometer: it can find very small amounts and identify new drugs that libraries don’t know yet. Both are lab methods, with results in days to weeks. As with GC-MS, a lab measures amounts only for the drugs it has standards for, and results don’t usually list sugars or other inactive cuts.

DART-MS (direct analysis in real time mass spectrometry)

A lab method that screens a sample for many drugs in seconds, including small amounts, without separating it first. NIST’s RaDAR program uses it to screen samples sent in by partner services, and tests some of them with LC-MS as well. It says which drugs are there, not how much.

NMR (nuclear magnetic resonance)

NMR reads the structure of the molecules in a sample. It can identify the main ingredients and measure how much is there without needing a reference sample for every drug. It is less good at finding very small amounts. A few labs use it.

What no test can tell you

• A negative result doesn’t mean a drug is safe. Strong drugs can be present in amounts too small to find, or unevenly spread.
• If the result is unexpected, it is okay not to use it, or to use much less.
• Start low and go slow. Try a small amount first, and wait longer than you think before taking more.
• Try not to use alone. If opioids could be involved, carry naloxone and know how to use it. It works on fentanyl and nitazenes (more than one dose may be needed), but not on xylazine or benzos.
• In an emergency, call 911 in the US and Canada. Many places have laws that protect people who call for help during an overdose.

This guide is general information, not medical advice. The people at a drug checking service can talk your results through with you.