Drug Driving Expert Witness Case Study 2

Independent forensic expert evidence in a drug-driving case

Bericon Forensics was instructed to provide independent forensic expert witness evidence in a drug-driving case involving cannabis, alcohol and an allegation of impairment.

The defendant had been driving a motor vehicle involved in a road traffic collision. Police officers reported that he smelled strongly of intoxicants, and a breath test later gave a positive result for alcohol.

A Forensic Medical Examiner assessed the defendant and formed the opinion that he was impaired. An attempt to obtain a blood sample was unsuccessful, so a urine sample was provided instead.

Laboratory analysis identified carboxy-THC in the urine. Carboxy-THC is an inactive metabolite associated with previous cannabis use.

The forensic expert’s instructions

A forensic toxicology expert witness was asked to review the scientific evidence and comment on:

• the significance of carboxy-THC in urine;
• whether the result demonstrated recent cannabis use;
• whether it could establish impairment at the time of driving;
• the absence of active THC from the sample; and
• the limitations of interpreting urine drug results.

Independent forensic toxicology review

The forensic expert explained that the detection of carboxy-THC supported previous cannabis use. It did not establish when cannabis had been used, how much had been consumed or whether the defendant was impaired while driving.

Urine testing is generally evidence of drug exposure rather than a direct measure of the concentration of an active drug in the bloodstream at a particular time.

The pharmacologically active cannabis compound, THC, was not detected. The available toxicology findings therefore did not provide direct scientific evidence that cannabis had caused impairment at the time of driving.

Expert witness conclusion

The forensic toxicology expert witness concluded that the urine result could not be used to determine the defendant’s mental or physical condition at the relevant time.

The scientific evidence supported prior cannabis use, but it could not show whether the defendant was affected by cannabis while driving.

Case outcome

The defendant was found not guilty.

This case demonstrates the importance of obtaining an independent forensic expert review where a drug result is being relied upon as evidence of impairment. The presence of a drug metabolite does not necessarily establish that an active drug was present or that it affected the defendant’s ability to drive.

Instruct a drug-driving expert witness

Bericon Forensics provides access to experienced forensic experts and expert witnesses for criminal defence cases involving:

• drug-driving allegations;
• driving while unfit through drugs;
• cannabis and THC interpretation;
• blood and urine toxicology;
• prescription and illicit drugs;
• alleged impairment;
• review of prosecution toxicology reports; and
• independent expert witness reports.

Our forensic toxicology experts can assess the scientific findings, explain the limitations of drug-testing evidence and prepare clear reports for solicitors, counsel and the court.

Contact Bericon Forensics to discuss the instruction of a drug-driving expert witness.