• A drug is a chemical substance that changes the way in which the body works, including our behaviour. Some drugs particularly affect the central nervous system and change our psychological behaviour.
  • There are different types of drugs:
    • Narcotic: is a drug that makes us feel sleepy.
    • Painkillers: blocks electrical impulses concerning pain from going up to the brain so we feel less pain.
    • Hallucinogens: Drugs like LSD can distort our senses of colour, time and space.
    • Stimulants: Speeds up reaction time as it increases the speed of neurotransmission (as more neurotransmitter is released).
    • Depressants: Slow down reaction times as it decreases the speed of neurotransmission (blocks the neurotransmitter receptors)
  • Drugs that are used to make people feel a certain way are recreational drugs (e.g. alcohol) and there are drugs used to heal people in medicine.
  • Some drugs are legal, some are only legal at certain ages and some are illegal because they are too addictive and dangerous.
  • Some people can get addicted to drugs – they feel a physical need for it.

Damage caused by smoking

  • Nicotine: a drug present in cigarettes which is the addictive part of tobacco smoke. This makes it difficult to give up smoking.


  • Tar is a sticky substance that contains chemical substances called carcinogens. These can cause cancers, which develop mostly in the lungs, mouth and throat.
  • It coats the lungs and as it thickens it reduces the surface area of alveoli. This means less O2 can diffuse into the blood.

Carbon monoxide

  • CO is a poisonous gas as it binds with the haemoglobin in the blood. This bond is 400 times stronger than the bond in oxyhaemoglobin, therefore it is impossible to remove. This therefore reduces the amount of O2 that can be transported in the blood.
  • A lack of oxygen to active muscles can cause pain, such as in the legs when walking.
  • CO also makes blood vessels narrower. Therefore, body cells by those blood vessels get even less oxygen and die. Dead tissues must be removed as they can be easily infected.

Paralysed cilia

  • Tobacco smoke can paralyse the cilia on ciliated cells in the trachea. This means they cannot do their job of wafting pathogens up the windpipe and therefore smokers more often get chest infections.


  • This is the build up of tar in the alveoli when it gets to the point that the layer is so thick the person cannot breathe properly and needs to get treatment.