Biology B1 - Drugs and You


Drugs and You

Drugs are chemicals that can alter the way the body works. There are different types of drugs, and they have different effects on the body.

Tobacco and alcohol are legal recreational drugs which have potentially serious effects on the body.

Illegal drugs are classified on a scale from Class A - the most dangerous - to Class C - the least dangerous.

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Drugs and You

Types of drugs

Drugs alter the way the body works. Some are beneficial, while others are harmful.

Depressant - Slows down brain activity - Alcohol, solvents, temazepam

Hallucinogen - alters what we see and hear - LSD

Painkiller - Blocks nerve impluses - asprin, paracetamol

Performance enhancer - improves muscle development - anabolic steroids

Stimulant - increses brain activity - nicotine, caffeine, ecstasy

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Drugs and You

Classification of drugs

Some drugs are legal, such as tobacco and alcohol. Others are illegal, or must only be prescribed by a doctor. Some prescription drugs are misused and taken for recreational use, rather than for medical reasons. They become illegal under these circumstances.

Illegal drugs are classified from Class A to Class C. 

  • Class A drugs are the most dangerous, with the most serious penalties for possession or dealing.
  • Class C are the least dangerous, with the lightest penalties, but this does not mean they are safe to use.
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Drugs and You

Stimulants and depressants

Stimulants and depressants affect the synapses between neurones in the nervous system:

  • stimulants cause more neurotransmitter molecules to diffuse across the synapse
  • depressants stop the next neurone sending nerve impulses – they bind to the receptor molecules it needs to respond to the neurotransmitter molecules.
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Drugs and You


Smoking can cause lung disease, heart disease and certain cancers, and around 114,000 people die every year as a result of smoking-related illnesses.

Cigarette smoke contains many harmful chemicals.

The cells lining the trachea (windpipe), bronchi and bronchioles (the branches inside the lungs) are damaged by cigarette smoke. These epithelial cells have tiny hair-like cilia on their surface. Normally these cilia move to push mucus out of the lungs. Damaged cells cannot do this, leading to a build-up of mucus and a smokers’ cough.

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Drugs and You

Carbon monoxide

Carbon monoxide combines with the haemoglobin in red blood cells and so reduces the ability of the blood to carry oxygen. This puts extra strain on the circulatory system, and can cause an increased risk of heart disease and strokes. Smoking during pregnancy is very dangerous. It reduces the amount of oxygen available to the growing fetus, which leads to an increased risk of low birth weights of babies.


Carcinogens are substances that cause cancer. Tobacco smoke contains many carcinogens, including tar. Smoking increases the risk of lung cancer, and cancer of the mouth, throat and oesophagus. 

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Drugs and You


The alcohol in alcoholic drinks - such as wines, beers and spirits - is called ethanol. It is a depressant. This means that it slows down signals in the nerves and brain. There are legal limits to the level of alcohol that drivers and pilots can have in the body. This is because alcohol impairs the ability of people to control their vehicles properly. Breath tests and blood tests are used by the police to see if a driver is over the limit.

Short-term effects

Alcohol has short-term effects such as sleepiness and impaired judgment, balance and muscle control. This leads to blurred vision and slurred speech. There is an increased flow of blood to the skin, which can cause it to become red.

Long-term effects

The long-term effects of alcohol include damage to the liver and brain.

The liver removes alcohol from the bloodstream. It has enzymes that break down alcohol but the products of the reactions involved are toxic. They damage the liver and over time this leads to cirrhosis.

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