Alcohol mainly affects the central nervous system by impairing intellectual, sensory and motor functions.

Intellectual functions

These are the first to be affected by alcohol, decreasing one's attention, self-control and ability to judge. 

Sensory functions

Hearing and especially sight are affected by alcohol, leading to:

• greater difficulty adapting to night vision and slower recovery from glare;
• modification of depth perception;
• a reduction in peripheral vision (tunnel effect);
• double vision when blood alcohol content reaches 100 mg alcohol per 100 millilitres of blood (mg%), an occurrence that is further amplified after surpassing 150 mg %.

Hearing is also impaired when one is inebriated.

Motor functions

Alcohol impairs muscle control and coordination, causing the following behaviour:

• staggering;
• difficulty in clearly pronouncing words;
• loss of manual dexterity;
• loss of precision in gestures and movements.

Driving a car is a complex activity which requires the execution of several simultaneous tasks.  The driver must be able to perceive, interpret and react to events, which proves difficult when faculties are impaired by alcohol!

Symptoms of alcohol impairment

Several symptoms appear when a person's abilities are weakened by alcohol.  In fact, police officers watch for them when deciding whether to make an arrest. If you notice such symptoms in friends, try to convince them not to drive, and more importantly, do not get in the vehicle with them.  If they still insist on driving, call 9-1-1!

• Irritated eyes
• Difficulty talking
• Difficulty standing straight
• Difficulty walking in a straight line
• Slow gestures
• Distracted behavior
• Slow response to questions
• Tendency to fall asleep
• Increased feelings of sadness
• Aggressiveness
• Ceaseless and exaggerated giggling
• Faster breathing
• More profuse perspiration
• Accelerated speech
• Louder talking

Sources: SAAQ and the École nationale de police du Québec

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