The rising cases of driving under the influence (DUI) incidents in Malaysia is not merely a legal crisis, it is a public health emergency.
Understanding the “neurological hijacking” that occurs during intoxication is vital for every driver.
DUI is the operation of a vehicle while chemically impaired.
While alcohol (ethanol) is the most commonly associated culprit, DUI also includes impairment by illegal drugs, prescription medications and over-the-counter substances.
These substances all act as central nervous system (CNS) disruptors.
Alcohol, for instance, is rapidly absorbed into your bloodstream and requires the liver to filter it at a rate of roughly one standard drink per hour.
If you consume substances faster than your body can metabolise them, your cognitive functions collapse.
Neurological breakdown
Driving or riding a motorbike requires the coordination of several brain regions.
Substances systematically “unplug” these circuits in a dose-dependent sequence:
- Blood alcohol concentration (BAC) 0.02%: Minor relaxation – the prefrontal cortex (the brain’s “CEO”) slows down, leading to a slight loss of judgement and declined visual tracking.
- BAC 0.05%: Lowered alertness – the cerebellum is affected, reducing coordination and steering precision.
- BAC 0.08%-0.10%: Impaired reasoning – muscle coordination drops significantly.
It becomes difficult to detect danger and reaction time to hazards is delayed.
- BAC 0.15% and above: Severe neuro-depression – the CNS undergoes widespread cortical suppression.
At higher levels, an individual may experience total loss of balance and severe oculomotor (i.e. movement related to the eyes) impairment.
This level induces “cognitive blindness”, where the brain can no longer synthesise sensory input into actionable data.
Your BAC is the ratio of alcohol to the water in your body, which is influenced by:
- Biological make-up
Women typically have less body water and more body fat than men, causing their BAC to rise faster.
- Food
Eating before drinking slows the absorption of alcohol into the small intestine, preventing a rapid spike in blood levels.
- Tolerance
“Holding your liquor” is a neuro-adaptation; it does not protect the brain from toxin-induced impairment.
“Go/No-Go” failure
The most dangerous effect is the disruption of the brain’s “start-stop” circuitry.
The “Go” system (D1 neurons) seeks reward, while the “No-Go” system (D2 neurons) acts as the brain’s braking mechanism.
Alcohol and drugs overstimulate the “Go”, while paralysing the “No-Go”.
Once this “brake” is offline, a driver becomes neurologically incapable of accurately assessing their own impairment.
Apart from alcohol, various substances can severely impair the cognitive and sensory functions required for safe driving:
- Stimulants (e.g. methamphetamine, cocaine) – these can lead to impulsive, aggressive driving and a dangerous overestimation of one’s abilities.
- Depressants and opioids (e.g. benzodiazepines, heroin) – these cause extreme drowsiness, slowed reaction times and “nodding off” at the wheel.
- Cannabis – this impairs spatial orientation, time perception and the ability to maintain a steady lane position.
- Prescription medications – certain medications can induce heavy sedation.
Because the part of your brain required to judge your sobriety is the very part that impairment disables first, you cannot trust your “feeling” of being sober.
When we weigh the cost of a ride-sharing service against the consequences of a DUI, the math is simple.
Taking a taxi or e-hailing car is a neuro-rational failsafe.
The choice to book a ride isn’t just a legal precaution; it is a rational act of self-preservation.
In the end, saving a life, including your own, is the only outcome that is truly worth it.
Associate Professor Dr Jayakumar Murthy is an addiction neuroscientist at Universiti Kebangsaan Malaysia. For more information, email starhealth@thestar.com.my. The information provided is for educational and communication purposes only, and should not be considered as medical advice. The Star does not give any warranty on accuracy, completeness, functionality, usefulness or other assurances as to the content appearing in this article. The Star disclaims all responsibility for any losses, damage to property or personal injury suffered directly or indirectly from reliance on such information.
