Drug driving, sedation, reaction time and blood levels: a prescriber’s approach to the Land Transport (Drug Driving) Amendment Act 2022

On 11 March 2023 the Land Transport (Drug Driving) Amendment Act 2022 (LTAA) came into effect.¹ This amendment introduced changes to the Land Transport Act 1998 and is part of the Road to Zero strategy, a plan from Waka Kotahi, the New Zealand transport agency, to reduce the number of deaths on roads in Aotearoa.² Data from the New Zealand Police indicate in 2021 there were 93 people killed in motor vehicle accidents where a driver was found to have drugs in their system—nearly a third of all fatalities that year.³ It can be surmised that the Act was in large part revised in order to address drug driving, in which those intended to be captured under the Act were using non-prescribed or illicit drugs. However, the broadening of scope to capture prescribed medications does not appear to have been thought through by legislators. No prescribers were consulted in the development of this legislation, resulting in the implications for prescribers currently being poorly defined. It is also important to view the risks in a larger context, particularly as the odds of causing an accident on only a benzodiazepine or an opioid is similar to the risk of driving a black car (univariate odds 1.2, multivariate odds 2.0).⁴

While it has long been illegal to drive impaired, the new Act identifies 25 drugs (21 that can be reasonably prescribed), defined in the Act as Schedule 5 drugs, and the blood levels of these drugs that are thought to impair driving (Table 1). Drivers that are found to be impaired can be charged. The Act also has additional penalties when drivers are found to have taken Schedule 5 drugs with alcohol or have multiple Schedule 5 drugs in their system.¹

View Table 1.

As part of the amended Act, drivers will have the option of a “medical defence” if they are found to have blood levels of Schedule 5 drugs above the pre-defined blood levels. This is defined as “… a way for you to dispute your drug driving infringement by providing evidence that you have taken your prescription medication in accordance with your current prescription, and any instructions from a health practitioner or manufacturer.”⁵ Patients will have to provide both a copy of the current and valid prescription for identified drug(s) and a copy of the label from the container in which the qualifying drug(s) were dispensed in, alongside any other relevant information they wish to have considered.

This shift in legislation requires patients to provide proof they have taken their Schedule 5 medications as prescribed. Therefore, prescribers have a duty to provide evidence-based advice on the possible effect of medication on driving, as well as any potential interactions/effects if prescribed medication is taken with other drugs (including over-the-counter medications) and/or alcohol. Should patients cause a motor vehicle accident while under the influence of medication, they will be exempt from prosecution under the LTAA, irrespective of the tested blood levels, if they can provide evidence that they have taken the medicine as prescribed. Practitioners cannot be charged under the same Act but could become subject to investigation and/or face liability by the Health and Disability Commissioner (HDC), the Medical Council of New Zealand (Medical Council) and/or the Coroner (in the event of a fatality).

As yet, there have been no cases in which this has happened. Nor has there been any guidance from governing bodies on how prescribers should incorporate the LTAA mandates into their practice. Thus, general good prescribing rules apply. The Medical Council describes good prescribing as being “… in accordance with accepted practice and any relevant best practice guidelines” in their 2020 statement on prescribing practice.⁶ Therefore, for practitioners to avoid being found liable by the above regulating bodies, they would have to know what accepted practice is. Currently, to the authors’ knowledge, there do not appear to be best practice guidelines for the prescribing and use of specific drugs or drug categories in relation to driving, other than Medsafe data sheets and the LTAA.

This article aims to clarify the available evidence for the effect of the prescribable Schedule 5 drugs on driving and provide guidance for prescribers on how to prescribe these medicines in context of the updated LTAA. This article specifically covers benzodiazepines, benzodiazepine-like sedatives (i.e., “z-drugs”) and opioids, as these are the Schedule 5 medicines commonly prescribed in Aotearoa.

Effects of benzodiazepines on driving

Benzodiazepines and benzodiazepine-like medications (hereafter referred to as just benzodiazepines) are extensively used internationally. In Aotearoa zopiclone was the 14th most frequently dispensed medicine in 2020. The most commonly dispensed benzodiazepines in 2020 were lorazepam and diazepam. Benzodiazepine use is prevalent in older adults, with approximately 10% of people aged 75 years and older regularly dispensed these medicines. As Papoutsis et al.⁷ pointed out, due to the high frequency of benzodiazepine use within the population, a zero-tolerance policy seems impractical despite the lack of experimental data indicating a safe cutoff for driving.

Benzodiazepines, like alcohol, work by modulating the effects of gamma-aminobutyric acid (GABA) by binding to the GABA_A receptor. By increasing GABA activity, benzodiazepines and alcohol have sedative, anxiolytic and anti-epileptic effects, and impact cognitive functioning. In this way, benzodiazepines and alcohol share similar pharmacodynamic properties, and it might therefore be useful for practitioners to conceptualise the effect of benzodiazepines as like the effects of alcohol on driving.

Several small (around 10 to 20 participants per arm) randomised controlled trials have shown that acutely, benzodiazepines have a significant negative impact on performance on various psychometric assessments.^7–11 These psychometric assessments are designed to identify individual brain functions affected, some of which are relevant to driving a vehicle such as psychomotor reactions or processing speed.^7–9,12 There are also many observational studies that have linked benzodiazepine use to crash risk in real-life settings both at therapeutic and supratherapeutic levels.^7,13,14 However, a meta-analysis that considered both prescribed and illicit benzodiazepine use was able to factor out multidrug use. For those using only benzodiazepines it showed a significant publication bias; when this was corrected for the odds ratio for involvement in traffic accidents, this was reduced from 1.65 (self-reported use risk) to 1.17, a much more modest risk.¹⁴

Studies regarding the effect of long-term (stable) benzodiazepine use on driving is scant. Van der Sluizen et al.¹¹ examined the effects of regular benzodiazepine use on both driving and neurocognitive tests outcomes in 100 volunteers and found driving test results were indistinguishable from controls after 3 years of consecutive use, but not before. Cognitive tests did, however, remain abnormal after driving tests normalised.¹¹ The subjective sedative effects of benzodiazepines often wear off well before the 1–3-year mark, thus indicating that a lack of subjective drowsiness is not a good indicator of safety for driving.

Effect of opioids on driving

Opioid pain relief is indicated for acute pain associated with injury or surgery, or pain secondary to malignancy. Use of opioids for chronic non-cancer pain is discouraged in most international pain management guidelines due to lack of benefit relative to the associated risks of long-term opioid use. However, there will be exceptions to this rule for various reasons, including opioid substitution therapy. The rate of opioid prescribing in Aotearoa has been relatively stable since 2013, with a slight downwards trend observed year-on-year, although an increased rate was seen in 2020–2021, which may reflect delayed surgeries during the COVID-19 pandemic lockdowns. Rates of opioid prescribing are higher for weak opioids than strong opioids; for example, in 2020 the rate of ≥1 codeine dispensing was 60 per 1,000 population, and the rate for morphine dispensing was 9 per 1,000 population. Overall, there is a general trend of higher opioid use in older adults, who may be particularly susceptible to adverse effects due to pharmacokinetic changes, polypharmacy and comorbidities, and in the context of driving typically have slower reaction times.¹⁵

Opioid medications bind to endogenous opioid receptors in the brain and spinal cord, blocking pain pathways and thus altering the perception of pain. In addition to a pain-relieving effect, agonism of the opioid receptor is also linked to the regulation of processing, mood, motivation, learning and memory and gastrointestinal function.¹⁶ Side effects of exogenous opioids include sedation, constipation, nausea, euphoria with acute use and depressed mood with more chronic use, respiratory depression and physical dependence.¹⁷

To what extent opioids affect a person’s ability to safely drive a vehicle was assessed in a recent review by Cameron-Burr et al.¹⁷ There was significant heterogeneity in the results, likely secondary to heterogeneity in study design, small sample sizes, publication bias and whether the opioid was prescribed or illicitly obtained. Overall, the majority (69%) of included experimental studies (i.e., prescribed rather than illicitly obtained opioids) found that opioids impair psychomotor function. There was evidence of a dose–response relationship between opioid therapy and impairment. While the authors of the review study did not do any statistical analysis, the summary of results suggests in many of the included studies there was approximately a twofold increased risk of impairment or motor vehicle accident compared to non-opioid using controls. This is consistent with the older meta-analysis from Elvik et al., who put the odds ratio of a fatal accident at 2.30, and 1.94 for accidents causing injury.¹⁴ Unfortunately, it was not possible to distinguish between prescribed and illicit use in the odds ratio because of a lack of data. However, data were for people who were identified to have had only opioids, which will have reduced the interference from the more extreme illicit use.

The impact of chronic use of opioids on driving is not well understood, and studies in this area have been small. Overall, the available results suggest that chronic use of prescription opioids does not impair driving; however, the tight inclusion criteria for these studies and small sample sizes make it difficult to generalise these results to the general population.¹⁷

Practical questions

Question 1: Can and should a practitioner assess for sedation and reaction time in a medical appointment?

In Aotearoa it is already common for general practitioners (GPs) or secondary care providers to make decisions around driving capacity for those with dementia or minimal cognitive impairment. It would be sensible to assume similar practice in driving capacity that may be affected by medications. The 2014 Dementia and Driving Safety clinical guideline¹⁸ states “Clinical bedside testing is a poor guide to deciding on a person’s driving safety”, and advises when there is doubt a patient should undertake an occupational therapist (OT) driving assessment through one of the local agencies. This advice is equally valid for those with impairment secondary to medication. If a clinician is uncertain about whether or not driving is impaired, such a test would be useful. The authors are aware some opioid substitution clinics have had their patients assessed with the aid of a Work and Income disability grant.

Question 2: Should practitioners be taking benzodiazepine or opioid blood levels to determine whether a patient should drive?

Measuring blood concentrations of Schedule 5 drugs to try to quantify risk is impractical, as most of the drugs listed in Schedule 5 do not have validated assays at community laboratories. As drug concentrations change over a dosing interval based on a drug’s pharmacokinetic characteristics, a single sample taken at a random time point is of little value in advising patients about suitability of driving, even when the question of active metabolites is not considered. Drug interactions, whether pharmacokinetic (e.g., inhibiting the clearance of a Schedule 5 drug) or pharmacodynamic (e.g., combining another sedative drug with a Schedule 5 drug) further complicate advice to patients. Drug concentrations for people who have yet to reach a steady state are particularly unhelpful in predicting future drug levels, thus making testing unhelpful in those who use pro re nata (PRN) doses.

Question 3: What should prescribers advise regarding interactions between two or more Schedule 5 drugs, or between Schedule 5 drugs and unlisted qualifying drugs?

The LTAA specifies an NZ$4,500 fine or up to 3 months imprisonment for driving under the influence of a single Schedule 5 drug, and NZ$6,000 or 6 months imprisonment for driving with two Schedule 5 drugs or combining alcohol with a Schedule 5 drug. It does not specify how many Schedule 5 drugs can be given before a medical defence can no longer be provided. In many cases the prescriber would not only need to think about the cumulative sedative effect of the prescribed medications, but also other pharmacokinetic and pharmacodynamic interactions.

Some medications can affect the blood levels of opioids and benzodiazepines by affecting their metabolism and clearance. For example, fluoxetine inhibits the conversion of codeine to morphine—meaning the plasma level of codeine may be elevated and the elimination half-life prolonged. Other substances, e.g., gabapentinoids, not only have effects on alertness and cognition, but have also been shown to reverse the tolerance to opioids when initiated in someone taking opioid medication.

Given the complexity of these factors alongside individual variation in drug response and metabolism, it is not possible to predict how use of two or more interacting substances will affect an individual. As such, it may be best to advise patients taking two or more medications that may increase the risk of impaired driving that they should not drive while taking these medicines.

Question 4: How long should patients not drive after taking PRN benzodiazepines or opioids?

Unfortunately, there is no published evidence that has looked at how many hours after taking a Schedule 5 medication effects on driving impairment are no longer present. Based on known medication principles it is likely that certain factors such as age and dose affect the duration of impairment. However, there have been no specific research studies into this.

Based on the paucity of specific evidence regarding this question, the most logical approach may be to use drugs’ half-lives to determine how long a person should not drive after taking medication. The debate on how many drug half-lives to use as a cutoff has no direct evidence to make a decision. The art of medicine is interpreting the available information and then applying it to a practical situation with a patient rather than waiting for such research to be published. It can be assumed that after 4–5 half-lives all medication will be cleared from the body. However, given how commonly Schedule 5 medications are prescribed in Aotearoa, using 4 half-lives as a rule would be very disruptive for many patients. In an attempt to balance clinical practicalities and pharmacokinetic principles, the authors suggest a more reasonable approach may be to use 2 half-lives (75% of medication cleared) as a general rule. However, for patients with renal or liver impairment, those who take doses higher than those recommended by Medsafe, the elderly, people using multiple medications, people who still feel sedated, people who are using PRN medication more than incidentally (i.e., more than 2–3 times a week) or for any other reason identified by the prescriber, it would be wise to recommend waiting 4 half-lives after taking the medicine before driving.

Practical recommendations for prescribers

1. Patients prescribed Schedule 5 medications should be advised to avoid any alcohol if driving, both due to possible additive effects and interactions and because using non-prescribed substances while driving might make their medical defence invalid.
2. Currently there is no recommendation for medical practitioners to do “bedside” reaction time testing or any other driving suitability tests. Patients could be referred for driving assessment.
3. There is little to no value in ordering blood levels of Schedule 5 medicines in a clinical setting.
4. It is useful that any instructions re driving are both put in the patient notes and on the prescription so the pharmacist can reiterate the advice to the patient.
5. If patients do feel sedated or tired, they should, of course, be advised to avoid driving. The general statement that it is safe to resume driving once a patient no longer feels sedated is common among medical practitioners and is taught during medical training. However, there is no empirical evidence to substantiate this for Schedule 5 medications, and there is some evidence that driving impairment on medication lasts longer than the subjective feeling of sedation.
6. For patients on stable doses of one Schedule 5 medication with no psychoactive polypharmacy, it would be good practice to inform the patients of the new LTAA rules. The authors would argue that a reasonable practitioner would not tell these patients that they could not drive.
7. For patients on multiple Schedule 5 drugs or one Schedule 5 drug and other psychoactive substances likely to qualify as unlisted qualifying drugs, and whose polypharmacy cannot be limited, it would be wise to get advice from a (mental health) pharmacist or a peer group around suitability to drive and document this carefully in the patients’ notes. In these cases, a driving assessment might be warranted, or it may be necessary to advise the patient that they should not be driving, and document as such.
8. For short-term or PRN prescriptions, it is likely most appropriate the patient is counselled not to drive until 2 half-lives have passed in simple cases and 4 half-lives in the exceptions mentioned in point 4, as no habituation to the impairing effects is likely to occur.
9. The authors suggest that until other guidelines have been developed, this article provides an outline of what a reasonable prescriber might do. If adhered to, this advice should provide a defensible position should a prescriber become the subject of an investigation or complaint related to the LTAA.

Discussion

The aim of this article is to aid prescribers in familiarising themselves with the updated LTAA and the implications for prescribing benzodiazepines and opioids. It also aims to identify what a “reasonable prescriber” might do when prescribing Schedule 5 medication. Currently, Medsafe data sheets do not have sufficient detail to support prescribers in offering advice to drivers about the potential for impairment, or when they should or should not drive. The common advice of not to drive if one feels drowsy is of little practical use, nor does it appear to be supported by research.

Individual clinicians will have to determine their own risk appetite when it comes to prescribing and advising patients on these medicines. Cautious prescribers who take a conservative approach to prescribing may be reluctant to offer medical exemptions to any patient taking opioids or benzodiazepines, especially given the current lack of clarity on how the HDC complaints committee, the Medical Council of New Zealand and coronial bodies will respond to incidents where someone with a medical exception causes a traffic accident. This lack of clarity is likely to cause high regional variability in approaches and thus negatively impact patients’ access to either the ability to drive or their ability to access required medical care, despite this being explicitly stated as something the new LTAA was intending to avoid.⁵ The recommendation for OT driving assessments may induce issues with equity relating to the inability to pay or physical access to testing and resources and potential for wait lists. It is recommended that improved tests or guidelines are developed to support practitioners (though the authors are aware of instances where Work and Income has supported people on opioid substitution to financially access an OT driving assessment).

For practical purposes, this article groups the Schedule 5 medications into three categories: benzodiazepines, opioids and others (THC amphetamine and ketamine). The latter are less frequently prescribed and therefore not covered in this article. It is notable that several other medications that may affect driving are sometimes used as sleep aids; anxiolytics or pain medication are not mentioned in the legislation. Examples of these include sedating antihistamines (e.g., promethazine), sedating antipsychotics (e.g., quetiapine and olanzapine) and gabapentinoid drugs (gabapentin and pregabalin). The LTAA makes reference to “unlisted qualifying drugs”, defined as “… a qualifying drug not listed in Schedule 5” and assigns similar penalties for both Schedule 5 substances or unlisted qualifying drugs.¹ However, there are no plasma concentrations provided for unlisted qualifying drugs. It is possible that there will be an increase in the use of these medications listed above or other unlisted qualifying drugs over Schedule 5 medications due to a (mis)understanding that drugs not on the Schedule 5 list will not result in legislative consequences for drivers. How the use of these drugs will be interpreted by judges and police is currently unclear. It is also possible that prescribers, in the light of this article, start viewing PRN prescribing as more risky than regular prescribing, which would be against guideline recommendations and might negatively affect patients.

It appears clear to the authors that prescribers cannot be held responsible for patients who continue to drive when the prescriber documents they are not supporting a medical exemption. However, how the HDC, Medical Council of New Zealand and coronial bodies will interpret prescribers giving medical exemptions to patients who they know, or could reasonably suspect, use recreational substances including alcohol also remains unclear, especially if these patients cause an accident on a combination of prescribed and recreational substances. It would be helpful if these regulatory bodies provided a position statement addressing these issues to help clarify prescriber expectations and responsibilities when prescribing these medicines.

How the legislation will be applied to specific situations remains unknown and will likely become clear over time, especially as the Government is in the process of developing the legislation to allow for roadside saliva testing. Guidance for clinicians and patients, including specific patient information leaflets that include application of the LTAA legislation in practice, would be useful, and would aid in the safe use of these medicines.

View Appendix.