Any drug or substance with effects on the central nervous system can impair the ability to drive safely.When prescribing, consider the effects of each drug on driving as well as the use of other substances. Advise the patient of the risks.Opioids, benzodiazepines, anticonvulsants, antipsychotics and sedating antidepressants increase the risk of crashing. Erratic use of sedatives causes a higher level of impairment than stable regimens.Patients who have complex medical conditions and take multiple drugs should undergo a fitnessto-drive assessment.
Random testingAt present, random roadside alcohol and drug testing occurs to a variable extent throughout Australia. Alcohol testing involves a screening breath analysis followed by confirmatory testing with highly sensitive and specific instruments. When a confirmatory sample cannot be obtained, blood testing may be required.Random roadside samples of saliva are tested for three substances:• delta-9-tetrahydrocannabinol (cannabis)• methamphetamine (commonly known as ice or speed)• 3,4-methylenedioxymethylamphetamine (MDMA, commonly known as ecstasy).These drugs were originally selected to avoid legal defences based on prescribed medicines. Screening is done at the roadside with an oral wipe. If the result is positive, an oral fluid sample is taken and sent for confirmatory testing. Cut-off concentrations for driving offences are set according to the Australian Standard (AS/NZS 4760-2019) or local policies.
Mandatory testingMandatory testing is required following a motor vehicle collision. Blood, and in some jurisdictions, urine, is collected. Samples are screened for commonly used substances including alcohol. If there is a positive indication, confirmatory tests are carried out. Observation of impaired driving behaviour in conjunction with blood sampling is generally required to prove the offence of driving under the influence, particularly for prescription drugs. Drug concentrations on their own do not predict individual driving ability due to the user developing tolerance to the drug.
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