In addition to the labelling and warning system, most Australian jurisdictions also have offences relating to driving under the influence of alcohol or other drugs . These offences usually require a level of impairment in driving capacity caused by alcohol or other drug use, with this assessed based on evidence of a driver’s behaviour witnessed by police or others. The common formula is driving under the influence of a drug so ‘as to be incapable of having proper control of the motor vehicle’ . In South Australia, the test is ‘so as to be incapable of exercising effective control of the vehicle’s 4. The DUI offences in New South Wales and Queensland do not define what ‘under the influence’ means in impairment terms. Western Australia and Victoria also have driving while impaired offences, which resemble the DUI laws but relate only to drugs other than alcohol.The regulation of road safety risks associated with the use of illicit drugs is the subject of drug driving legislation in each Australian State and Territory, which, in turn, is informed by the National Road Safety Strategy . In all States and Territories, road safety legislation specifies a group of substances for which it is an offence to drive with any amount in a person’s bodily fluids, regardless of impairment. These offences are loosely referred to as ‘presence offences’. Because any detectable amount in the driver’s system constitutes an offence, Australian jurisdictions have been described as having a ‘zero tolerance’ approach to drug driving . Although just the presence of these drugs is an offence, in practice, minimum detection thresholds have been adopted to control for accidental exposure, often reflecting the detection and quantification limits of the roadside drug testing devices and analytical instruments employed by the police and forensic services. These thresholds vary across jurisdictions. Drivers can alternatively be charged with the DUI and DWI offences referred to in the section above if a police officer reasonably suspects that a person’s driving ability has been impaired by an illicit drug.
Although jurisdictional approaches vary, in practice, a person would not be charged with both a presence and a DUI/DWI offence in relation to the same incident. In NSW for example, there is a specific double jeopardy defence which prevents a person from being charged and convicted for a both a DUI and a presence offence simultaneously . DUI/DWI offences involve more severe penalties, but due to greater complexity in prosecution would rarely be used if a person can be charged with the presence offence. Enforcement of presence offences for illicit substances is most commonly conducted via roadside oral fluid drug-testing regimes . Presence offences are also enforced through mandatory blood tests, which are administered to any driver admitted to a hospital following a road accident in which a person is injured . Typically, grow cannabis in containers only three illicit drugs are tested for in oral fluid: THC; MDMA; and methamphetamine. New South Wales added cocaine to this list of drugs tested for in oral fluid in 2018. While presence offences apply overwhelmingly to illicit drugs, Tasmania and the Northern Territory include a much larger number of drugs – most illicit, but some of which could be medically prescribed.No Australian jurisdiction currently tests for the presence of prescription drugs in preliminary oral fluid tests conducted at the roadside, with the examples above being tested for in secondary testing. Notably, in some Australian jurisdictions there exists a medical defence for having the presence of certain drugs with potential therapeutic application in blood or oral fluid, if they have been prescribed by a doctor and taken in accordance with a prescription. In New South Wales, this medical defence covers morphine and, in the Northern Territory, morphine, methadone and amphetamine and ; Traffic Regulations 1999 reg 55A, Schedule 1A – Part B.
In Tasmania, the medical defence covers any drug referenced in the legislation if it was obtained and administered in accordance with the Poisons Act 1971 , including medicinal cannabis Act 1970 s 6A; Road Safety Regulations 2018 s 15. To be clear, these medical defences provide an exemption to presence offences, but not the DUI or DWI offences that exist in Australian States and Territories. Other than Tasmania, there is no medical defence for patients prescribed medicinal cannabis taking it as directed and who are not impaired.The application of presence-based drug driving offences, originally designed to combat road safety risks associated with the use of illicit drugs, to patients receiving legal medicinal cannabis treatment has started to gain some policy attention in Australia. A recent Australian Senate Inquiry considering barriers to patient access to medicinal cannabis recommended a review of current ‘presence-based’ drug driving offences . However, in states other than Tasmania , road safety agencies remain opposed to any change in the treatment of medicinal cannabis, due to concerns about the potentially impairing effects of THC. When a bill to change this situation in South Australia was introduced to its parliament in 2017, the Police Minister labelled it ‘crazy’ and ‘inconsistent’ with road safety objectives . The bill was not passed. The National Drug Driving Working Group recommended no change to current legislative arrangements in 2018, with reference to the 0.00 BAC alcohol requirement for some groups of drivers . The key areas of concern for road safety agencies include possible impairment and elevated crash-risk associated with legal medicinal cannabis products, and the potential for misuse and supplementation by patients. We discuss these issues in turn below as well as the patient impacts of the current regulatory framework.The studies discussed above are only of partial relevance to medicinal cannabis as none have differentiated between medical and recreational use. There are several characteristics of medicinal use that may lead to a lower road safety risk among patients than among recreational users. In Australia, patients accessing legal medicinal cannabis are doing so under the supervision of a doctor and the goal of this treatment is to achieve a clinical benefit using dosing strategies that can avoid unwanted psychoactive side effects, such as a low commencing dose and slow upward titration .
This contrasts to most recreational use, which specifically relates to obtaining a psychoactive effect. Driving under the influence of cannabis is also associated with being a young, male adult, a subpopulation holding ‘high risk’ attitudes towards driving and an elevated crash risk irrespective of cannabis use . The demographic profile of the average Australian medicinal cannabis patient is notably different, with available data provided by the TGA indicating the majority of patients are female and over 50 years of age . Older drivers with physical ailments are also known to reduce their driving exposure, generally only driving during the day and in locales they know well, leading to a lower crash risk than younger age groups . A further potential risk reduction factor relates to the harm-benefit assumptions that underlie the usual prescribing of potentially impairing medications, and potential offsetting of increased road safety risks . In medicinal cannabis patients, substitution away from drugs with known impairing effects, including benzodiazepines and opioids, has been documented, with one study reporting that 45% of medicinal cannabis patients taking benzodiazepines at baseline had ceased use of these drugs at six months, while another found large reductions in opioid use among chronic pain patients . Similarly, improvements in clinical symptoms following treatment with THC may offset any detrimental cognitive effects, either directly or indirectly. Such outcomes have been reported for Sativex, the one medicinal cannabis medicine containing THC listed on the Australian Register of Therapeutic Goods. Both driving simulation and large patient registry studies of Sativex have identified no evidence of increased accident risk . A recent review investigating the acute effects of THC on driving-related cognitive skills, primarily for recreational use, also identified a small number of studies in clinical populations, which reported mostly non-significant subtle positive or negative effects on driver impairment. The authors suggest this evidence of minimal impairment associated with medical use may reflect lower doses typically administered in a medical context and the likely amelioration of clinical symptoms that had been causing impairment .
While experimental studies investigating the effect of medicinal cannabis on driving ability remain limited, a number of US epidemiological studies have examined road safety risks specifically associated with legal medicinal cannabis, by analysing changes in road accident data after the introduction of such access schemes. Using fatal crash data from 2010–2017 in US states, Cook et al. found that in states with ‘medical cannabis only’ frameworks the move away from prohibition was associated with fewer total fatal crashes for both males and females. A similar finding was reported by SantaellaTenorio et al. , however some variation among states was noted. Other studies have examined change in the prevalence of fatally injured drivers testing positive to THC , however this measure is problematic as detecting presence after an accident relies on the use of blood samples . Hence, an increase in the proportion of fatally injured THC positive drivers may simply reflect a greater proportion of the population having used cannabis at some time in the last week , without signalling impairment, causality, or recent use. Nevertheless, studies looking at this metric have also in general found no significant increase in the proportion of fatally injured drivers testing positive for THC in states moving to ‘medical cannabis only’ access models, although exceptions for some states or supply types have been noted . Other research has also reported a reduced presence of opioids among fatally injured drivers aged 21 to 40 in states introducing medical cannabis legalisation , suggesting a potential substitution effect . It is worth noting that the findings above have been reported in US states with much more permissive medicinal pot for cannabis schemes than Australia’s prescription only access model, with less regulation and quality controls governing access to these products.
There is also some evidence that tolerance to the acute effects of cannabis develops over time in regular users, resulting in less pronounced cognitive impairment in several domains related to driving, such as divided attention and time perception . As patients are typically taking the medication daily, a level of tolerance to these impairing effects would be expected. Available evidence suggests tolerance development is primarily pharmacodynamic, resulting from neuroadaptive changes in the brain rather than from users adjusting their behaviour to compensate for any impairing effects . However, in relation to psychomotor abilities, evidence suggests the development of tolerance to impairment relating to psychomotor coordination, but not other psychomotor processes such as response speed, sustained attention, visual spatial skills and set shifting . As such, the development of tolerance to impairing effects in patients could be expected to partially, but not fully, diminish potential effects on driving skills compared with an occasional recreational cannabis consumer taking a similar dose.Concerns about the potential misuse of prescribed medicinal cannabis are relevant to consider given the serious safety issues that currently exist around other prescription medications such as opioids and benzodiazepines .
In addition to misuse, supplementation with a chemically indistinguishable illicit version of the substance , orblack-market prescription cannabis products, would also be possible. The widespread availability of illicit/recreational cannabis creates a somewhat different risk profile compared with other prescription medications such as opioids or benzodiazepines, where risk is more likely to be associated with misuse or overuse of prescription products. While both misuse and supplementation of medicinal cannabis are possible, there are some factors that may mitigate these risks. In contrast to other medicines with a risk of misuse, no medicinal cannabis products are currently subsidised via the Pharmaceutical benefits Scheme , meaning that patients need to pay the full cost of the product themselves, which is higher than the street price of illicit cannabis . As a result, there is little financial incentive for the diversion or overuse of prescribed medicinal cannabis products.Conversely though, the high cost of medicinal cannabis products may provide an incentive for patients to either supplement their prescription with illicit cannabis or substitute their prescribed medication with an illicit cannabis product.