Are you confident that anything you buy over the counter at the chemist must be safe and will not affect your driving? Wrong!
In this article, you’ll find out which easily available over-the-counter products can affect you, as well as which prescription drugs.
Driving is a complex information-processing task. It’s one of the most challenging activities people engage in on a daily basis. A lot of information has to be processed quickly and acted upon.
The three human factors needed for safe driving are vision, cognition (the ability to think clearly) and motor function (the ability to physically take action), in other words: perception, decision making and reaction.
All of the above factors can be impaired by age, medical conditions, medication, illegal drugs, alcohol, fatigue, inattention, distraction or emotional states, resulting in a crash.
Studies have shown that human performance errors are the most common causes of motor vehicle accidents. There are three factors involved in crashes:
*These figures don't add up to 100%, as there is some overlap in causes.
Recognition errors (problems in perception and comprehension) and decision making errors were most frequently implicated in a study.
Medication can have a positive or negative effect on driving.
On the plus side, an older driver with untreated depression is at high risk due to decreased concentration and slower decision making, so treating this person helps them drive more safely. Treating diabetes will also improve performance and eyesight.
However, treatment may also carry a risk. For instance, 10mg of diazepam (or Valium) for anxiety can produce more driving impairment than a blood alcohol concentration of 0.10% (the limit in New Zealand is 0.05%).
A Montreal study of over 224,000 drivers aged 67-84 found that those on long-acting benzodiazepines (tranquillizers) had 45% more collisions resulting in injury.
Medicine combinations can produce unexpected side effects. You need to discuss all your over-the-counter medications with your family doctor. The interaction between alcohol and over-the-counter medications can also be a problem.
With age, tolerance for alcohol decreases. Then, if you add medication, risk increases even more. If you add medical conditions or multiple medical conditions to the mix, the risk increases again.
Adding a new medication may change the way other medications are handled by the body, so you must give yourself two weeks to settle into your new medication or combination of medications.
The side effects of medications can be incredibly varied. Among the more common are sedation, nausea, impairment of vision, hearing or concentration, dizziness, low blood pressure, fainting and loss of co-ordination.
Any of them can bring risk, but the most frequent culprits are:
Since 90% of driver information is visual, blurred vision is a major risk factor. Blurred vision can be caused by:
Reduced ability to see at night may result from:
Cognition, especially attention, working memory, visuospatial abilities, and visual search are essential to safe driving. This can be affected by:
Motor and muscle abilities are important in driving, e.g. for physical muscular activities such as fast reaction, braking, steering, etc.
Older medications show negative effects in 89% of studies, compared to 10% for newer ones.
Medications you can buy over the counter cause some of the most common and serious impairments due to their widespread use and because of the common belief that, because these medications are available without prescription, they must be safe. Any drug that depresses the central nervous system can potentially impair driving. Mostly they are for:
A single product can have several drugs that increase impairment, e.g. a pain reliever combined with a decongestant. Sleep helpers contain old-fashioned antihistamines which are sedating, e.g. diphenhydramine is found in Sleep Gels and Calm U.
Older people buying medications over the counter are more vulnerable for various reasons, as their slowed kidney function slows the eradication of the drug from the body, so the drug accumulates. Watch out for:
Paracetamol such as Panadol is fine to use.
Drugs & Driving PDF (258KB)
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