As a leading provider of legally-instructed drug testing, we are frequently asked to explain how a sample donor could test positive for a substance they claim never to have used.
These queries are increasingly common, particularly in family law cases where drug testing is used to assess parenting capacity, monitor abstinence, or confirm compliance with court orders.
Legal professionals may receive a toxicology report showing one or more drugs not disclosed by the donor and not anticipated at instruction. While the accuracy of the analysis is not in question, such results can raise serious concerns – especially where the donor’s denial appears credible.
The illicit drug market is increasingly characterised by contamination and deliberate mixing of substances. Users are often unaware that what they are taking has been cut with, substituted for, or combined with other drugs, some of which are significantly more potent or harmful.
This means that, in some cases, a toxicology report may show the presence of drugs the donor did not knowingly consume.
What is poly drug use?
Poly drug use refers to the use of two or more substances within a given timeframe. This may be deliberate – to enhance or moderate effects – or unintentional, where a drug has been contaminated or mis-sold.
Some combinations have street names. ‘Calvin Klein’ (or CK), for example, refers to the concurrent use of cocaine and ketamine.
With no regulation or quality control in illicit drug manufacturing, substances are routinely cut or laced with others to increase profit margins or intensify effects.
At AlphaBiolabs, we have seen a rise in samples testing positive for multiple drug groups. For family law professionals, this highlights the importance of instructing comprehensive toxicology testing, including screening beyond standard panels, particularly where behaviours or symptoms cannot be explained by a single substance.
How are street drugs contaminated?
Illicit drugs are often adulterated with other drugs, masking agents or bulking agents such as sugars. Of growing concern is the rise of synthetic opioids, particularly nitazenes, in the UK drug supply.
In 2022, the Advisory Council on the Misuse of Drugs (ACMD) reported that over 25% of cocaine samples and more than 50% of heroin/diamorphine samples seized in the UK contained isotonitazene, a powerful nitazene analogue. Separately, Public Health Scotland has linked another nitazene, ‘Pyro’ (N-pyrrolidino etonitazene), to a sharp rise in drug-related deaths across Scotland (August 2025).
In such cases, a positive test result may reflect contamination rather than deliberate use – a distinction with significant legal implications.
One such example at AlphaBiolabs involved a donor (Mr X) whose hair sample tested positive for five substances: THC, cocaine, norcocaine, benzoylecgonine, and ketamine.
While Mr X accepted the presence of the other substances, he strongly denied taking ketamine, saying:
“I haven’t even seen ketamine. I don’t know anyone who uses it, or even how to use it. I would not be able to get it if I tried – I don’t have a horse, and I’m not a vet!”
How AlphaBiolabs can support your case
AlphaBiolabs is an award-winning, UKAS 17025 and Lab 51-accredited laboratory with 20+ years’ experience supporting family law professionals, social workers and local authorities.
We provide legally-admissible drug and alcohol testing using a range of sample types, including hair, nails, blood, oral fluid, urine, and breath, with bespoke repeat testing schedules available.
We also test for the widest range of substances including the most-abused drugs as well as ‘non-standard’ drugs e.g. steroids, prescription medications, hallucinogens, nitazenes, other emerging synthetic opioids. Custom testing panels can be created to suit your case.
And with our Price Promise, where we will beat any like-for-like quote by a further 10%, you know that you are guaranteed to get the best value for money.
To request a quote, contact our New Enquiry team on 0333 600 1300 / testing@alphabiolabs.com or complete our online quote form www.alphabiolabs.co.uk/legal-test-forms/.
