Cross-Reactivity and False Positive Safeguards in Drug Testing
Case reference FOI2026/01574
Received 7 July 2026
Published 10 July 2026
Request
I am writing as a follow-up to my recent Freedom of Information request regarding drug testing safeguards in substance misuse services commissioned or operated by your authority.
Since submitting that request, I have become aware of additional published evidence regarding the known limitations of immunoassay-based drug screening — the type of point-of-care test routinely used in workplace and service settings across the UK.
Specifically, peer-reviewed literature confirms that lawful, everyday substances can produce false positive results on these devices.
Documented sources of cross-reactivity include poppy seeds, over-the-counter CBD products, prescribed medications (including codeine, tramadol, gabapentin, and certain antidepressants), tonic water, bananas, passive or environmental exposure to cannabis smoke, and certain antihistamines — among others.
These are not theoretical risks. They are reproducible, documented in clinical and forensic toxicology literature, and well known to laboratory professionals.
In light of this, I am requesting the following additional information under the Freedom of Information Act 2000:
1. Is your authority (and/or its commissioned substance misuse service
provider) aware of the cross-reactivity risks identified above? Has any assessment been made of the likelihood of false positive results from lawful sources when using immunoassay screening?
2. Does the applicable drug and alcohol testing policy require that all positive screening results are confirmed by a second, independent analytical method — specifically GC-MS or LC-MS/MS — before any disciplinary, safeguarding, or service-access decision is made?
3. If confirmatory testing is not routinely carried out, on what basis are positive screening results treated as definitive?
4. Has your authority (and/or its provider) received any complaints, grievances, or representations from individuals who attributed a positive drug test result to any of the lawful sources listed above?
If so, how many in the last three years, and what was the outcome?
5. What guidance, if any, has been issued to staff involved in drug testing about the possibility of false positives from lawful substances, and the appropriate steps to take before acting on a screening result?
I would prefer to receive the information electronically where possible. If any part of this request is unclear, I am happy to clarify. I understand you are required to respond within 20 working days.
Response
I am writing as a follow-up to my recent Freedom of Information request regarding drug testing safeguards in substance misuse services commissioned or operated by your authority.
Since submitting that request, I have become aware of additional published evidence regarding the known limitations of immunoassay-based drug screening — the type of point-of-care test routinely used in workplace and service settings across the UK.
Specifically, peer-reviewed literature confirms that lawful, everyday substances can produce false positive results on these devices.
Documented sources of cross-reactivity include poppy seeds, over-the-counter CBD products, prescribed medications (including codeine, tramadol, gabapentin, and certain antidepressants), tonic water, bananas, passive or environmental exposure to cannabis smoke, and certain antihistamines — among others.
These are not theoretical risks. They are reproducible, documented in clinical and forensic toxicology literature, and well known to laboratory professionals.
In light of this, I am requesting the following additional information under the Freedom of Information Act 2000:
1. Is your authority (and/or its commissioned substance misuse service
provider) aware of the cross-reactivity risks identified above? Has any assessment been made of the likelihood of false positive results from lawful sources when using immunoassay screening?
2. Does the applicable drug and alcohol testing policy require that all positive screening results are confirmed by a second, independent analytical method — specifically GC-MS or LC-MS/MS — before any disciplinary, safeguarding, or service-access decision is made?
3. If confirmatory testing is not routinely carried out, on what basis are positive screening results treated as definitive?
4. Has your authority (and/or its provider) received any complaints, grievances, or representations from individuals who attributed a positive drug test result to any of the lawful sources listed above?
If so, how many in the last three years, and what was the outcome?
5. What guidance, if any, has been issued to staff involved in drug testing about the possibility of false positives from lawful substances, and the appropriate steps to take before acting on a screening result?
I would prefer to receive the information electronically where possible. If any part of this request is unclear, I am happy to clarify. I understand you are required to respond within 20 working days.
Answer: The information for question 4 is not held in a form that would enable it to be located, retrieved and extracted within the Appropriate Time Limit which equates to 18 hours as defined by the Freedom of Information and Data Protection (Appropriate Limits and Fees) Regulations 2004.
Our electronic reporting systems are unable to run a report for this information. To ascertain the data requested, officers would need to manually check individual files for this information. An initial search has shown that 389 files would need to be checked for this information, and it is estimated that it would take 5 minutes to check each file. Once the details had been identified this would need to be noted and once all files had been checked in this way, the total figures requested could be calculated.
This would at a conservative estimate take at least 32 hours to complete. Where the Limit is exceeded Public Authorities are not obliged to supply the information requested by virtue of S12 of the Act. Please take this letter as a refusal notice under S17 of the Act.
However, within the 18 hour limit, we can provide answers for all remaining questions as requested. Please advise us if this is something you require.
Documents
This is Herefordshire Council's response to a freedom of information (FOI) or environmental information regulations (EIR) request.
You can browse our other responses or make a new FOI request.