Alcohol is the most common drug of abuse in the world. In fact, it is said that if alcohol was discovered today it would be scheduled as an illegal drug. However, history tells us that alcohol has been used and drunk since the time of the Summerians five and a half thousand years ago, and probably before that.

It was not until the 20th century that alcohol and its effects have been studied to understand what happens in the body and the human brain to such an extent that it is the most researched drug ever. There is a plethora of information about alcohol on the web, some of it good but a lot of it bad and anecdotal, so be careful what you believe.

800px-Ethanol-3D-vdWFor the purpose of this section, however, we need to concentrate on the effect that the drug has in the workplace and on driving.

Alcohol that we drink is called ETHANOL (ETOH) and is made up of 2 carbon atoms, an oxygen atom and six hydrogen atoms. (Seen here looking like a pudgy dog!.)

There are many compounds known as ‘alcohol’s.’ For example, Ethylene-Glycol is found in antifreeze, Wood Alcohol or METHANOL can be drunk and is found in Turpentine (frequently abused and causes blindness as the methanol turns to formaldehyde in the eyes)

The Ethanol molecule is relatively small compared to a molecule of Morphine. But a standard can of beer or a short will have 200 quintillion ethanol molecules each of which can disrupt some part of the body’s cells.

When you take on alcohol it is immediately digested. In other words alcohol is a diuretic, meaning that it does not have to enter the stomach before it begins to metabolise. But when all is said and done, alcohol is poisonous to the human body which is why it does its utmost to get rid of it as soon as possible as soon as it touches your lips.

It will happen in three stages (not that you’d notice of course) The first line of defence is a detoxylising enzyme called alcohol dehydrogenase. (ADH)

ADH removes the hydrogen atom from our ethanol molecule

This is now called acetaldehyde and it renders the ethanol inactive

But AH is still dangerous to the body and can bind with proteins to cripple normal function.

A second enzyme comes into play

Aldehyde dehydrogenase (AHDH) This destroys AH and turns our molecule into Acetic Acid, which is harmless and you naturally get rid of.mThis is all done in the liver as the alcohol passes through. Excess alcohol causes sclerosis of the liver, making it hard and unable to process and clean the blood.

So how does all this affect the brain and our ability to do things. Alcohol sits in the Depressant category of drugs (see page ?). This is because at high doses alcohol slows down the central nervous system, when the classic symptoms of drunkenness can be seen. If fact it can depress the CNS so much that breathing will stop.

But not only does it depress, it also causes behaviours that are more like the effects of a stimulant. So in short alcohol depresses the higher cognitive functions of the brain, but also stimulates those functions associated with disinhibition for example.

These feeling of pleasure and euphoric effects underlies much of alcohols’ addictive potential. It releases endorphins that tap into the brains pleasure circuits and affects everything around it.

Whatever the case units of alcohol cannot be artificially reduced by the liver. A government unit of alcohol is approximately 15% of the ethanol you have ingested. What does this mean in practice?  For example If you started drinking a bottle of wine with a meal at 7pm and drank half the bottle, finishing off with a double whiskey, it could be calculated like this:

½ bottle of wine = 5 units + Double whiskey = 3 units = Total units = 8

The liver would have completely metabolised the ethanol by 3 am in the morning.

REMEMBER that 1 Unit = 1 Hour to metabolize

So you could estimate, in the above example that you would be free from alcohol by 3am. There are however no guarantees. And from the point of view fo a driver, there is no certainty that they would be under the driving limit before those 8 hours have passed.

It is however common today for people to drink in excess of 8 units in an evening. A phenomenon known as ‘pre-loading,’ common among young people probably means that they would have had 5 – 10 units before their evening started in earnest.

Many driver’s have been caught out when driving to work the following morning and find themselves providing a positive breath test when required to do so by a police officer. (See Blog)

Example - Friday Evening
      • Pre-loaded drinks – 6 Units
      • ½ bottle of wine – 5 units
      • series of shots – 10 units (1 shot = 1 unit)
      • 3 double vodka – 9 units
      • night-cap (Home measure) – 4 units
    • Stops drinking at 2 am

Total units 34 units

Free from alcohol 34 hours after stopping drinking around midday on Sunday!


Medium strength Lager = 3 units
Bottle of wine = 10 units
1 measure of spirits (35ml) = 1.5 units

Beating the breath test

Myths that just will not go away. The modern digital breathalyser cannot be fooled. It is designed to seek out the alcohol in your breath and nothing will hide it. And these myths, below? well… that’s what they are!


Sucking on a copper coin
Drinking black coffee
Eating a large meal
Chewing on an alkaline battery – Yuck!
Eating garlic
Using a breath freshener (most are alcohol based!)
I’m OK with just a couple of pints!