Drug testing has revealed that products sold as heroin, diazepam, and cannabis often contain potent synthetic opioids and other unexpected substances. In Wales, the Welsh Emerging Drug Identification Service (Wedinos) found that more than one in three samples submitted between April 2025 and March 2026 did not contain the substance the buyer had expected. This highlights a growing issue in the illicit drug market, where the name, appearance, or packaging of a drug may not reflect its actual contents. One of the most concerning discoveries was the presence of a new group of synthetic opioids called "orphine analogues." These are highly potent substances, meaning even small doses can have powerful effects. This poses a particular risk when someone believes they are taking heroin but is actually consuming a different, potentially more dangerous substance. The report found that orphine analogues were often found alongside veterinary sedatives in samples submitted as heroin. While the specific toxic effects of this combination are not yet well understood, the presence of multiple unexpected substances makes the risks and effects harder to predict. This issue is not limited to Wales. The UK government has classified seven of these orphine substances as class A drugs under the Misuse of Drugs Act 1971, following reports that they were linked to at least 22 deaths. Similar substitution problems are also appearing in the illicit cannabinoid market. Wedinos found that 43% of vape samples labeled as THC, CBD, or cannabis-related products contained "spice" instead. These synthetic substances mimic the effects of cannabis but can be more intense and unpredictable, leading to severe reactions like anxiety, hallucinations, and seizures. The substitution of substances is widespread across the illicit drug market. Wedinos continues to identify other potent synthetic opioids called nitazenes in their samples. In products sold as diazepam — a common sedative known by the brand name Valium — synthetic benzodiazepines have been found. Meanwhile, products sold as cannabis vapes often contain synthetic cannabinoid receptor agonists (SCRAs), also known as "spice." This means that users may not be able to rely on traditional cues such as the name, color, or packaging to identify the substance they are taking. Many of these products are purchased through illicit online channels, including fake pharmacies, and can look identical to legitimate medicines. This makes it difficult to distinguish between an illegal drug and a counterfeit medicine. While an illegal drug is knowingly purchased as an illicit substance, a counterfeit medicine is designed to mimic a legitimate pharmaceutical product. This confusion increases the risk that people may unknowingly take substances they did not intend to use. Drug checking services like Wedinos play a crucial role in harm reduction by analyzing samples and identifying the substances they contain. This information helps track emerging trends and substitutions that might otherwise go unnoticed. However, drug testing has its limits. It can only confirm the contents of a specific sample and does not guarantee that other products from the same source contain the same substances. While drug checking cannot provide absolute safety, it helps reduce uncertainty. As the illicit drug market becomes more complex, the information provided by these services is becoming an essential tool in harm reduction efforts.