Dec 29, 2021

How do testkits work?

“Analytical chemistry” can be a bit of an intimidating term, and is probably a poor choice as the first two words in this article, but it doesn’t need to be. All it really means is using chemistry to understand the substance you’re looking at. To do some punk analytical chemistry, all you need is a few bottles of testing reagent.

In the lab, one technique often used by scientists for this purpose is to fire a beam of light through the sample. They then observe the different frequencies of light which come out the other side to calculate what chemicals must be present in that sample. You may not have access to the kit required for that, but you can still become an “analytical chemist” with your testing reagents to take drugs more safely.

When you mix your sample with specific chemicals, the chemical reaction that results is visible to the naked eye. This won’t give you the same precise results as the lab-based approaches but you can use it as a “qualitative test”, answering the question of “is X drug present?” with a yes or no. In this article, I will explain how drug testkits work, so you can become an analytical chemist and find out what’s in your drugs.

The exact mechanism varies from reagent to reagent. In a nutshell, we’d say that the chemicals in the testing reagents react with the drugs in our samples, forming new compounds which respond to light differently. As an example, let’s look at the workhorse of the reagent world: Marquis reagent. This surprisingly simple stuff is made with just two ingredients: sulphuric acid and formaldehyde. Sulphuric acid is mostly used in making fertilizers, cleaning chemicals, etc. Formaldehyde is used in making things like plywood and adhesives. We believe formaldehyde is key in the process.

We say “we believe” because we’re not actually sure specifically how it works. We think that the ring-shaped structures highlighted below (phenyl group) bind with the formaldehyde. Then, the colour of the light that we see depends on the rest of the structure of the drug. Let’s give a couple of examples. A drug like MDMA absorbs most light and looks really dark, while 2C-B absorbs specific parts of the light and reflects yellow and green light back, which is what we see.

Here we see 2C-B (top) and MDMA (bottom), with the phenyl groups which bond to the formaldehyde.


This is why Marquis reagent is so useful: it can bond with a huge variety of drugs and identify broad classes. This helps you to decide which reagents you should use next to identify whether you actually got what you paid for or something else entirely - it’s a lot more common than you might think! Whether someone just made a mistake and mixed up a baggy, or someone’s deliberately selling some cheaper drug (NEP and methylone as major examples), this kind of substitution has been rife for a long time, but the globalisation of the market and explosion in research chemical production has caused these kinds of practices to become commonplace.

You might be wondering why you’re suddenly hearing so much about testkits and drug checking in the last few years, and this is why. The simple truth is that while they’ve always been incredibly useful, they’re more important than ever because the drug market is getting worse. Substances like fentanyl and black market benzos/gabapentinoids are leading to skyrocketing drug deaths1, and the MDMA market is at its most unreliable in over a decade 2.

Why? This is a complex problem, but many of the decisions of our governments and the actions of law enforcement are contributing to make drug markets more harmful. For instance, attacks on online drug markets have irreparably damaged the little supply-side quality control that was available 3. Moreover, destroying the top end of the MDMA supply has made the whole psychostimulant market more dangerous 4. Likewise, cracking down on the legal provision of opioids and benzos has only done more damage, pushing people into buying on the black market. Some of those people are legitimately relieving their medical conditions and some aren’t, but all of them are in more danger now than ever before 5.

These strategies are having catastrophic effects on both the drug markets themselves and the ways in which you interact with them. As a result, it falls to you to protect yourself and your friends with harm reduction tools like these little kits.

Get your drug testkits here. If you use this link, 5% of sales are for Drugs and Me, which supports our content and software development.


1 McPhillips, Deidre (2021). Drug overdose deaths top 100,000 annually for the first time, driven by fentanyl, CDC data show. CNN. Accessed: 29 Dec 2021.

2 Scally, Cameron (2021). The Rise and Fall of the Superpill. Dosetest. Accessed: 29 Dec 2021.

3 FBI (2017). Darknet Takedown FBI. Accessed: 29/12/2021

4 Townsend, Megan (2021). Experts warn of 'fake MDMA' circulating in Manchester Mixmag. Accessed: 29 Dec 2021

5 Crackdown. Episode 20: cut off. Crackdown. Accessed: 29 Dec 2021.

This article was written by Cameron Scally

Cameron is the content director for DoseTest, a worldwide social enterprise which provides reagent testkits and fentanyl test strips as widely and cheaply as possible. You can find them at @dosetest on Twitter or @dosetestofficial on Instagram for a regular dose of information about testing, harm reduction and the world of drugs.