Section 10

Psychiatric disorders

Some patients with a diagnosis of schizophrenia have slowed cognitive processing. They may also have a variable degree of distraction that will typically depend on the perceptual distortions present at the time. Edlund et al. (1989) concluded that individuals with schizophrenia who drove had double the risk of motor vehicle crashes per distance driven compared with age-matched controls. Many of the cognitive impairments associated with this condition have been shown to improve with treatment, somewhat more so with atypical than with typical antipsychotic medications.

Cuesta et al. (2011) reported on the usefulness of two brief cognitive screening tools for determining the presence of cognitive impairment in patients with schizophrenia or bipolar disorder: the Brief Cognitive Assessment Tool for Schizophrenia (B-CATS; Hurford et al., 2011) and the Screen for Cognitive Impairment in Psychiatry (SCIP; Gómez-Benito et al., 2013). Both brief testing instruments showed good to excellent concurrent validity, relative to a Global Cognitive Composite Score derived from a more comprehensive testing methodology, and seem to be reliable and promising tools, although not directly predictive of on-road driving performance; they may be useful resources in assessment of selected cases.

Patients who are taking their prescribed medication, are not actively hallucinating, and have no active delusions, thought disorder, or cognitive or motor adverse effects from antipsychotic medication are generally fit to drive. If there is clinical reason to doubt fitness to drive, an on-road evaluation is recommended.

Personality disorders constitute a more controversial area. The locus of distress is often with others, not with the individual who has been given the diagnosis. The behavioural pattern is defined as persistent, and the diagnosis often has a pejorative or dismissive tone. This attitude is unfortunate, because there have been many advances in recent years that provide good evidence for the treatability, and sometimes cure, of conditions such as borderline personality disorder.

Some personality disorders, including antisocial, borderline, and narcissistic personality disorders, may be associated with behaviours such as aggression, egocentricity, impulsiveness, resentment of authority, intolerance, and irresponsibility. Police reports, if available, or other reliable third- party observations may assist the physician in making fitness-to-drive recommendations for patients with these conditions. Please also see Section 10.4.7, Aggressive driving, and Section 16.2, Moderate to severe TBI, for information about driver aggression.

Some individuals with mood disorders, even when treated and achieving full remission, continue to have some residual cognitive dysfunction that affects short-term memory, concentration, or mental processing speed. The SCIP (described in Section 10.4.1) is an appropriate screening tool that may be used to assess for the presence of cognitive impairment in patients with depression as well as schizophrenia.

A manic episode is a contraindication to driving. Fitness to return to driving will depend on response to treatment and the patient’s level of insight and of inter-episode functioning. If a patient with bipolar disorder is advised not to drive, consent should be sought to notify a family member, and any such communications should be documented. Non-compliance with medical advice not to drive should be reported to licensing authorities.

Most treatment of depression is with newer-generation drugs rather than the older tricyclic agents (Kennedy et al., 2016). Tricyclic antidepressants have been associated with an increased risk of motor vehicle crashes, especially at higher doses or if multiple agents are used (Rapoport et al., 2011). Theoretically, selective serotonin reuptake inhibitors and other newer-generation antidepressants have a pharmacologic profile associated with lower risk of cognitive impairment, but evidence in the literature is less clear (Yang et al., 2016).

As reported by Hill et al. (2017), 

Antidepressants have potentially conflicting contributions to motor vehicle crashes in relieving the effects of depression and suicide while posing side effects that may affect driving. While the benefits of antidepressants outweigh their potential risks, prospective studies are needed to better understand the risk of antidepressants and depression on motor vehicle crashes. ...

In determining the effects of depression and antidepressants, it is difficult to distinguish effects of depression from effects of drugs [from studies published to date]. ...

Based on the reports of the studies included in this analysis, depression and antidepressants pose a potential hazard to driving safety. Physicians and other health providers, including pharmacists, should recognize the inherent risks of both the disorder and medications on driving and educate their patients accordingly. More research is needed to understand the individual contributions of depression versus the medications used to treat depression and to identify strategies to mitigate the effect of both on driving safety.

A challenging issue for investigators is that interpretation of this research is limited by indication and channelling bias (Petri and Urquhart, 1991). Channelling is a form of allocation bias, whereby drugs with similar therapeutic indications are prescribed to groups of patients with prognostic differences. The general principles outlined in this section and especially the alert box should be of foremost consideration.

Electroconvulsive therapy (ECT) may induce sustained confusion in 1 of every 200 patients (McClintock et al., 2014; Johns Hopkins University, Department of Psychiatry and Behavioral Sciences, 2017). Those receiving outpatient ECT need to comply with standard guidelines for not driving after anesthesia and should take extra time to recover before returning to driving if they are experiencing any memory problems after ECT.

Rapid-rate transcranial magnetic stimulation (rTMS) is reported to produce no evidence of cognitive impairment when used for treatment of depression. In fact, Turriziani et al. (2012) reported greater memory improvement among patients with mild cognitive impairment relative to healthy controls after administration of rTMS to the dorsolateral prefrontal cortex.

Aduen et al. (2015) contrasted the driving risks associated with adult attention-deficit/hyperactivity disorder (ADHD) and those associated with depression relative to those of a typical peer control group. Depression, but not ADHD, predicted increased risk for self-reported injury following collisions (relative risk ratio, 2.25; 95% confidence interval [CI], 1.05–4.82) (see also Section 10.4.6, Attention-deficit/hyperactivity disorder).

Because of frequent comorbidity, patients with a diagnosis of mood or anxiety disorders should also be screened for ADHD.

Anxiety disorders may cause motor vehicle crashes when the driver’s level of anxiety interferes with concentration or causes “freezing” or perseverative errors.

Severe motor vehicle crashes commonly lead to the development of psychiatric disorders. When symptoms of posttraumatic stress disorder or phobic avoidance complicate the picture, crash survivors can get significant help in the healing process through counselling and from relevant books. Ehlers et al. (2007) described the Driving Cognitions Questionnaire, a screening tool for identifying drivers with significant phobia, which is common among the general population and more common after a motor vehicle crash. This 20-item scale measures three areas of driving- related concerns: panic-related, crash-related, and social.

A meta-analysis by Rapoport et al. (2009) showed that benzodiazepine users were at a significantly increased risk of motor vehicle crashes relative to non-users. This difference may be accounted for by difficulty in maintaining road position.

Although benzodiazepines may increase the risk of motor vehicle crashes, low-dose clonazepam (1.0–2.5 mg/d), which is sometimes a useful primary maintenance treatment for panic disorder (Nardi et al., 2013; Perna et al., 2016), is unlikely to do so.

Psychotic episodes due to any psychiatric or general medical condition may be the most urgent psychiatric situation in relation to fitness to drive. An acute psychotic episode is incompatible with safe driving. Physicians should note that an acutely psychotic patient may be able to mask symptoms initially.

Any driver who has experienced an episode, including commercial drivers with Class 4 licences (e.g., taxi drivers), may be safe to return to driving once the acute episode has settled, if there are no impairing effects from maintenance medication and if there is sufficient insight to adhere to treatment and identify early indicators of relapse.

ADHD is not, in itself, a contraindication to driving. However, the motor vehicle licensing authority, as well as the parents of an adolescent with a diagnosis of ADHD who qualifies for a driver’s licence, should pay close attention to speeding, red light infractions, and risk-taking behaviour. Online resources may help with practical advice about risk reduction, including some novel technological monitoring approaches (Aduen et al., 2019; Norloff, 2020).

Although ADHD is now seen as a lifelong disorder, the prevalence decreases somewhat with age.
It is unclear why this is the case and whether it may reflect learned adaptive strategies. ADHD in childhood and ADHD in adulthood share many polygenes, which suggests that the genetic etiology is almost the same as the childhood presentation and is persistent (Rovira et al., 2020).

For both children and adults, psychostimulant medication may have a useful role in controlling symptoms and improving performance on a number of tasks. Stimulants have the most evidence supporting their efficacy in reducing the risk of moving violations and crashes for drivers with ADHD, particularly in the first 5 years of driving. The long-acting preparations of psychostimulants provide medication coverage throughout both the day and early evening and are formulated in ways that make them less likely to be diverted for illicit use.

As summarized by Barkley (2018),

ADHD in teens and adults is consistently associated with less safe driving habits, deficient driving performance, and greater inattention and impulsivity while driving. The disorder is also linked to more adverse driving outcomes, such as a greater risk for traffic citations (especially for speeding) and more of such citations; license suspensions/revocations; and a greater risk for crashes, more crashes, more severe crashes; and being found at fault in such crashes. Some of these adverse outcomes are also linked to and exacerbated by comorbidity with oppositional defiant disorder, conduct disorder or antisocial personality disorder.

A multisite study using large general population samples (Aduen et al., 2015) contrasted the driving risks associated with adult ADHD and with depression relative to those of a peer control group. Accounting for demographic differences, ADHD but not depression was associated with about twice the risk for multiple violations (relative risk ratio, 2.27; 95% CI, 1.48–3.49), multiple collisions (relative risk ratio, 2.21; 95% CI, 1.31–3.74), and collision fault (relative risk ratio, 1.65; 95% CI, 0.98–2.78). The authors concluded that adult ADHD is uniquely linked to increased adverse driving outcomes that are not evident in depression and are clearly greater than risks seen in healthy adults in the general population.

Texting on cell phones while driving markedly worsens the driving performance of teens, both those with ADHD and those without the disorder (Narad et al., 2013; Kingery et al., 2015; Llerena et al., 2015).

Chang et al. (2014) studied the association between ADHD and the risk of a serious motor vehicle crash (defined as an emergency hospital visit or death due to a motor vehicle crash) and explored whether ADHD medication influences this risk among patients with the condition. This study showed that drivers with ADHD had lower risk for a motor vehicle crash when they were taking medication than when they were not.

In a later study, Chang et al. (2017) showed that up to 22.1% of motor vehicle crashes involving patients with ADHD could have been avoided if they had received medication for the entire follow-up period.

Dr. Laurence Jerome developed the Jerome Driving Questionnaire (JDQ), now hosted by the Canadian ADHD Resource Alliance (https://www.caddra.ca/wp-content/uploads/JDQ.pdf); this resource is in the public domain.

Law enforcement agencies are paying more attention to ticketing aggressive drivers as the hazards associated with “road rage” become more evident. Individuals with ADHD are more likely to manifest anger, hostility, and aggression while driving, and such emotional dysregulation is also a factor in their crash risk (Richards et al., 2002, 2006; Barkley, 2018). Such behaviour is not exclusive to those with a diagnosis of ADHD and may be associated with a range of diagnoses, including mood and personality disorders, alone or in combination with each other or with ADHD. See also Section 16.2, Moderate to severe TBI.

Redelmeier et al. (2010) conducted a population-based case–control study in Ontario to examine the amount of road trauma involving teenage male youth that might be explained by prior “disruptive behaviour disorders” (specifically, ADHD, conduct disorder, and oppositional defiant disorder). A history of disruptive behaviour disorders was significantly more frequent among patients with trauma than among controls, equal to a one-third increase in the relative risk of road trauma. The risk explained about 1 in 20 crashes, was apparent years before the event, extended to those who died, and persisted among those injured as pedestrians.

With the present state of knowledge, it seems reasonable to refer aggressive drivers with insight for specialized cognitive behaviour therapy groups, where available. Those without insight will likely be dealt with only by court-ordered treatment and administrative prohibitions from driving, although motivational interviewing strategies may be of some benefit.