Annex 2 – Drugs and Driving Committee report on drug per se limits
Establishing a drug per se limit does not imply all drivers below this limit are not impaired and all drivers above this limit are impaired.
Impairment can be defined as a decreased ability to perform a certain task; this differs from intoxication which can be described as the observable signs of drug use.
The primary psychoactive compound in cannabis products is tetrahydrocannabinol (THC).
THC impairs the ability to operate a motor vehicle.
THC is the most frequently encountered drug in Canadian drivers, after alcohol.
THC and alcohol are frequently detected in combination in drivers.
Although the scientific literature varies, several well-controlled studies with sufficient discriminating power have demonstrated an increased crash risk in THC-positive drivers. Risks were increased for fatal collisions and with elevated THC concentrations.
Available evidence suggests significantly increased risks for drivers positive for alcohol and THC in combination.
Unlike alcohol, the effects of THC do not correlate well with THC blood concentrations.
Impairment due to THC is related to the amount, the route of administration, the time elapsed since use, and inter-individual variability.
Existing per se limits for THC vary widely between jurisdictions.
The THC per se limits considered by this committee are 5 ng/mL and 2 ng/mL in blood.
The 5 ng/mL THC per se limit is based upon impairment considerations, while the 2 ng/mL THC per se limit is based upon public safety considerations.
This committee recommends the use of distinct but corresponding per se limits for plasma.
This committee recommends a combined offence of 50 mg of alcohol in 100 mL of blood when detected in combination with THC at a concentration less than the limit for the THC alone offence.
Minimizing time delays in sample collection is critical to implementation of an effective THC per se limit.
Consideration of THC per se limits is complicated by the potential for prolonged THC blood concentrations in chronic users although there is evidence of residual impairment in this population.
The potential for passive exposure to THC resulting in concentrations at or above a per se limit is not a practical concern in the context of the conditions that would be required, the levels discussed and the inevitable time delay to sample collection.
Cocaine is a central nervous system stimulant which impairs the ability to operate a motor vehicle. Cocaine is susceptible to degradation in the body and in a collection tube; therefore, timely collection, preservative and proper storage conditions, and timely analysis are important. This committee recommends a cocaine per se limit of 30 ng/mL in the blood. No limit is recommended for benzoylecgonine, the inactive breakdown product of cocaine.
Gammahydroxybutyrate (GHB) is a drug which demonstrates central nervous system depressant activity in a dose dependent manner. GHB impairs the ability to operate a motor vehicle. GHB is also a compound that occurs naturally in the body at low levels, and as such, the per se limit must reflect a concentration above endogenous levels. This committee recommends a GHB per se level of 10 mg/L in the blood.
Heroin is an opioid analgesic which has central nervous system depressant properties. Heroin impairs the ability to operate a motor vehicle. Given the extremely short time frame for heroin detection in the body due to the rapid metabolism of heroin to its active metabolite, 6-monoacetylmorphine (6-MAM), this committee recommends zero tolerance for 6-MAM detection in the blood.
Ketamine is a dissociative anaesthetic which impairs the ability to operate a motor vehicle. This committee recommends zero tolerance for ketamine detection in the blood.
Lysergic Acid Diethylamide (LSD) is a potent hallucinogen which impairs the ability to operate a motor vehicle. This committee recommends zero tolerance for LSD detection in the blood. LSD is susceptible to degradation in a collection tube as it is light and heat labile; therefore, proper storage conditions and timely analysis are important.
Methamphetamine is a central nervous system stimulant which impairs the ability to operate a motor vehicle. This committee recommends a methamphetamine per se limit of 50 ng/mL in the blood.
Phencyclidine (PCP) is a dissociative anaesthetic which impairs the ability to operate a motor vehicle. This committee recommends zero tolerance for PCP detection in the blood.
Psilocybin is the compound present in ‘magic’ mushrooms which are used for hallucinogenic purposes; psilocin is the primary psychoactive metabolite of psilocybin. Psilocybin/psilocin impairs the ability to operate a motor vehicle. This committee recommends zero tolerance for psilocybin and/or psilocin in the blood.
Any drug recommended for zero tolerance in a blood sample is also recommended for zero tolerance in a serum or plasma sample.
Since zero tolerance will be related to the limits of the methodology employed, this committee recommends that the provincial and federal government forensic laboratory systems develop a common limit of detection for the aforementioned drugs so as to ensure the Criminal Code offence will not vary between jurisdictions.