Visual effects

There are multiple adverse visual effects of drugs that can affect driving. These include impaired scanning, depth perception (judging distance), reduced peripheral vision, ability to focus, or ability to track moving objects. Glaucoma drugs as eye drops cause temporary blurred vision. However, other medications may have a more prolonged effect. Examples include amiodarone, anticholinergic drugs (e.g., atropine, oxybutynin), and drugs used to treat erectile dysfunction. 

Motor effects

Motor effects can include slowed reflexes, so a person’s reaction times are slowed, or muscle weakness. Some psychotropic medications (and prochlorperazine) can cause movement disorders including Parkinsonism, dystonia (involuntary contraction of muscle groups that lead to repetitive or twisting movements in the body) and akathisia (restless legs syndrome). These effects generally disappear if the medication is stopped.

Cognitive effects

Sedation or drowsiness are commonly understood effects of medications, but drivers may fail to recognise drug-induced insomnia which leads to excessive daytime drowsiness as a factor in MR SID. Lack of alertness with or without feeling drowsy may also be present. This may affect the ability to divide attention between tasks and to process multiple sources of information; the ability to make rapid, appropriate decisions (processing speed); the ability to read the traffic environment; and reduced vigilance. Drugs may also impair short-term or working memory and can affect speech leading to trouble forming sentences or slurred speech.

Psychotropic drugs are not all sedatives – some act as stimulants and may lead to an increase in risk-taking behaviours, overconfidence and poor speed control.