New UK figures show that drug driving overtakes drink driving as a cause of driving convictions.
The figures were published by IAM RoadSmart on 9 July 2026 following analysis of DVLA data. They showed that 30,707 drug driving offences were recorded on driving licences during 2025, compared with 29,769 drink driving offences.
This does not mean that every incident of drug driving or drink driving was detected. However, it does show the increasing importance of forensic toxicology evidence in criminal cases.
What does a positive drug driving blood result show?
A positive blood result shows that a laboratory detected and measured a particular drug in a blood sample.
Under section 5A of the Road Traffic Act 1988, it is an offence to drive with the concentration of a specified controlled drug above the prescribed limit.
Specified drugs include cocaine, cannabis, ketamine, MDMA, methylamphetamine and a number of prescription medicines.
A result above the legal limit may provide evidence supporting a prosecution. However, the result does not necessarily establish how impaired the driver was.
Does a positive result prove impairment?
A prosecution under section 5A is based on the concentration of the drug in the blood. The prosecution does not usually need to prove visible impairment.
This differs from a prosecution under section 4, where the issue is whether the driver was unfit to drive through drink or drugs.
A blood result may therefore show that a legal limit was exceeded without showing the exact degree of impairment.
Why does the sampling time matter?
Blood samples are often taken some time after driving.
During this period, the concentration of a drug may change as it is absorbed, distributed and eliminated by the body.
The result must therefore be considered alongside the time of alleged driving, the time of sampling, the drug involved, the route of administration and the driver’s account of use.
For many controlled drugs, it is not possible to carry out the same type of reliable back calculation that may be available in alcohol cases.
Cocaine and cannabis results
In cocaine cases, the laboratory may report both cocaine and benzoylecgonine. Cocaine can indicate relatively recent use, while benzoylecgonine usually remains detectable for longer.
The relationship between the two results may help an expert assess whether an account of use is scientifically plausible.
Cannabis cases usually involve Tetrahydrocannabinol (THC). THC levels can rise quickly after smoking or vaping and then fall significantly. A blood concentration above the prescribed limit may support a prosecution, but it does not provide a precise measure of impairment.
How can Bericon assist with drug driving cases?
Bericon Forensics can arrange an independent review by a suitably qualified forensic toxicologist.
The expert may:
✔ review the laboratory report
✔ consider the timing of use and sampling
✔ assess whether the driver’s account is plausible
✔ examine measurement uncertainty
✔ comment on the significance of drugs and metabolites.
The expert may also consider alleged drug use after driving, prescription medication and whether the evidence supports impairment.
How can Bericon assist with drink driving cases?
Bericon can also arrange expert assistance in drink driving cases involving breath, blood or urine results.
This may include:
✔ review of breath test documentation
✔ alcohol back calculations
✔assessment of drinking after driving
✔ comparison of the stated drinking history with the evidential result.
The expert may also consider whether the driver was likely to have exceeded the prescribed limit at an earlier time.
Independent forensic advice
The finding that drug driving overtakes drink driving highlights the growing role of forensic evidence in road traffic cases.
A positive drug driving result may show that a legal limit was exceeded, but it does not necessarily establish the exact time of use or the degree of impairment.
Drink driving evidence may also require careful review of the result, the sampling process and the driver’s account.
Bericon Forensics works with criminal defence solicitors throughout the UK to arrange independent expert review in both drug driving and drink driving cases.
