5.1 Chemical Impact of Alcohol on the Body

Why the Chemistry Matters to a Duty Manager

A duty manager is not a doctor, but the Sale and Supply of Alcohol Act 2012 requires you to recognise intoxication and prevent it. You cannot do that reliably from a memorised checklist of signs unless you understand why those signs appear. This section covers the basic physiology that every other part of US 16705 Outcome 1 builds on. US 16705 names the "standard industry texts" as its benchmark, and those texts are the Te Whatu Ora – Health New Zealand publications hosted at resources.alcohol.org.nz: The Manager's Guide (AL575, current edition October 2023), the On-licensed Premises Toolkit, and the Host Responsibility Guide (August 2022). Check the edition date before relying on any downloaded copy — older PDFs of the same titles are still in circulation.

Alcohol Is a Depressant, Not a Stimulant

The single most common exam trap is calling alcohol a stimulant. Ethanol is a central nervous system (CNS) depressant. It slows neural activity. The early 'lift' or talkativeness a drinker feels is disinhibition — the cerebral cortex, which normally restrains behaviour, is being slowed down first, so inhibitions drop before motor and speech centres noticeably degrade. As consumption continues, the depressant effect spreads to motor coordination, judgement, memory and eventually the brainstem's vital functions.

Absorption, Distribution and Metabolism

Once swallowed, alcohol is absorbed mainly through the small intestine and to a lesser extent the stomach, then enters the bloodstream and is distributed throughout the body's water. It reaches the brain within minutes. Distribution is proportional to body water, which is why body size and composition (covered in 5.2 and 5.3) change blood alcohol concentration for the same intake.

The liver metabolises about 90–95% of the alcohol consumed. The key enzyme is alcohol dehydrogenase (ADH), which converts ethanol to acetaldehyde and then to acetate. Metabolism proceeds at a fixed rate of roughly one standard drink (10g of pure alcohol) per hour — this rate is not meaningfully increased by coffee, food, water, exercise, or a cold shower. The remaining 5–10% is excreted unchanged through breath, urine and sweat, which is why breath and urine can be used to estimate blood alcohol.

The 'Sobering Up' Myth

Because metabolism is fixed, a patron who has consumed six standard drinks needs roughly six hours to clear the alcohol regardless of what they do in the meantime. This is the scientific basis for the host-responsibility rule that you cannot speed up sobriety — you can only stop further service, offer food and water, and arrange safe transport or a place to wait. Telling a patron 'have a coffee and you'll be right' is both physiologically wrong and a licence-risk for the premises.

Effects on the Brain

Alcohol affects brain regions in a roughly predictable order, which maps directly onto the intoxication signs a duty manager watches for:

The medulla effect is why very high consumption can be fatal — alcohol can depress breathing to the point of death. A patron who has moved from 'loud and clumsy' to 'slumped and barely rousable' is a medical emergency, not just a refusal-of-service situation.

Effects on the Body

Beyond the brain, alcohol produces several systemic effects a duty manager will notice:

• Vasodilation — small blood vessels near the skin widen, causing the flushed face and feeling of warmth. Because blood is redirected to the skin surface, the body actually loses heat faster, so 'wine warms you up' is misleading; core temperature drops.
• Diuresis — alcohol suppresses the release of antidiuretic hormone, so the kidneys produce more urine. This causes dehydration and contributes to the headache and thirst of a hangover, and explains why offering water is not just hospitality.
• Gastrointestinal irritation — alcohol irritates the stomach lining, which is why drinking on an empty stomach can cause nausea and why food helps tolerance.
• Liver load — the liver prioritises alcohol metabolism over other tasks. Chronic heavy drinking leads to fatty liver, inflammation and cirrhosis.

Why a Duty Manager Needs This

Every visible sign of intoxication you will assess in Chapter 8 — slurred speech, loss of coordination, flushed appearance, mood change — has a biological cause traced in this section. Knowing the cause tells you three things the exam expects you to demonstrate:

1. The signs are progressive. They appear in a roughly predictable order as more brain regions are affected, so early signs (cortex effects) are your window to intervene before cerebellum and medulla effects appear.
2. Time is the only remedy. No intervention by the premises can sober a patron quickly; the duty is to stop service and manage safety.
3. Individual variation is large. Two patrons drinking the same amount present differently because of absorption and distribution factors covered in the next two sections.