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When someone buys a drug illegally, they cannot be sure exactly what is in it.

More than one in three samples submitted to the Welsh Emerging Drug Identification Service (Wedinos) where the buyer had said what substance they believed they had purchased, contained something other than what they expected. Between April 2025 and March 2026, 36.6% of samples submitted to Wedinos did not contain the expected substance.

These findings illustrate how the illicit drug market is often defined by substitution, where the name, appearance or packaging of a drug may tell us surprisingly little about what is actually inside it.

One of the most concerning findings in the latest Wedinos report is the identification of a new group of synthetic opioids known as “orphine analogues”. Synthetic opioids are chemically produced drugs that can have effects similar to opioids such as morphine and heroin.

Orphine analogues are highly potent types of synthetic opioids, meaning they can have powerful effects at very small doses. That creates a particular risk when someone believes they are taking heroin but is actually consuming a different, potentially more potent substance.

The findings are particularly concerning because orphine analogues were identified alongside veterinary sedatives in samples submitted as heroin. The significance is not necessarily that this particular combination has a unique or established toxic effect, but that someone believing they have bought heroin may instead be exposed to multiple unexpected psychoactive substances, making the effects and risks much harder to predict.

The concern is not confined to Wales. The UK parliament has been told that orphines had been implicated in at least 22 deaths. The government has added seven of the substances to the list of class A drugs according to the Misuse of Drugs Act 1971.

The problem, then, cannot simply be described as people choosing to use a new synthetic opioid. In some cases, people may have no idea that it is present.

Substitution is occurring across different parts of the illicit drug market. Wedinos continues to identify nitazenes, another group of highly potent synthetic opioids, in the samples they receive.

Novel benzodiazepines, synthetic central nervous system depressants, have been found in products sold as diazepam, commonly known by the brand name Valium. And products sold as THC, CBD or cannabis vapes have contained synthetic cannabinoid receptor agonists (SCRAs) , sometimes known as “spice”.

The result is a market in which people buying illicit drugs cannot necessarily rely on the usual cues used to identify them, like the name, colour, tablet shape, packaging or claims made by a seller.

Many of these products had been bought through illicit online routes, including fake pharmacies. They could look identical to legitimate medicines despite containing something other than the advertised drug.

Fake medicines

This is where it is useful to distinguish between an illegal drug and a counterfeit medicine. An illegal drug may be purchased knowing that it is an illicit substance. A counterfeit medicine is different because it’s deliberately manufactured and packaged to look like a legitimate pharmaceutical product.

The danger is that people may not realise they are taking an unknown substance at all. They may believe they are taking diazepam because the tablet and packaging look convincing.

The same problem is appearing in the illicit cannabinoid market. Wedinos found that 43% of THC, CBD or cannabinoid vape samples submitted to the programme contained spice rather than what consumers expected.

These are not ordinary nicotine vapes from legitimate shops that have unexpectedly been contaminated. They are illicit cannabinoid products, purchased through illicit routes and sold as THC, CBD or cannabis-related products. In other words, someone may believe they have bought a particular cannabinoid product but instead receive a different psychoactive substance.

Substances known as spice are designed to act on the same cannabinoid receptors as cannabis but can produce much stronger and less predictable effects.

When used in vape liquids, their effects can be rapid and intense, including severe anxiety, panic, hallucinations, psychosis and seizures. Someone can believe they are buying cannabis but instead receive a completely different psychoactive substance.

Why is this happening?

There is no single explanation for why substances are being substituted. Illicit drug markets respond to factors including price, availability, supply chains, policing and changes in legislation. New psychoactive substances can also emerge quickly, particularly when existing compounds become controlled or harder to obtain.

Drug checking services like Wedinos provides an important form of harm reduction by analysing individual samples and identifying what they contain. Such data can reveal emerging substances and substitutions that might otherwise remain invisible. But drug testing has limits. A test tells us what was identified in a particular sample and cannot guarantee that another tablet, powder or vape from the same seller or batch contains the same substances.

Drug checking is not a guarantee of safety. But it can reduce uncertainty. And as illicit drug markets become more complex, that information is becoming an increasingly important part of harm reduction.

Joseph Janes does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.