Sometimes people become dependent or addicted to a drug.  Without them, they would suffer withdrawal symptoms.

All drugs are broken down by the liver.  Too much of any drug can therefore cause liver damage.

Solvents are found in glues and paints. They are depressants.  This means they slow down the speed of impulses along nerves. 

Sniffing solvents is called solvent abuse.  It affects behaviour and can stop the lungs and heart from working.  It can also damage the liver and brain.

Alcohol is another depressant drug.  It affects the nervous system by slowing down reactions and may lead to a lack of self-control, unconsciousness or even coma.

Alcohol is an addictive drug and alcohol abuse can cause liver and brain damage.

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Harmful Effects of Smoking

Tobacco smoke contains many harmful chemicals.

Nicotine is the addictive drug in tobacco smoke.  It also narrows the blood vessels and can lead to high blood pressure and heart disease.

Tar can cause lung cancer and it irritates the airways in the lungs causing coughing.

Carbon monoxide is a poisonous gas that reduces how much oxygen can be carried in the blood.

Normally, oxygen attaches to haemoglobin in red blood cells to be transported around the body, as shown below:

oxygen  + haemoglobin → oxyhaemoglobin

Oxyhaemoglobin breaks down and releases the oxygen at the respiring tissues.

In smokers, carbon monoxide attaches irreversibly to the haemoglobin forming carboxyhaemoglobin, taking the place of oxygen.  This is why smokers often become breathless. 

carbon monoxide + haemoglobin → carboxyhaemoglobin

In pregnant women, this can deprive the foetus of oxygen leading to a low birth mass.

Smokers are also more likely to suffer from other lung diseases such as bronchitis and emphysema.  Bronchitis is an inflammation of the lining of the bronchioles, making it harder to breathe.  Emphysema is caused by excessive coughing which tears the delicate walls of the alveoli.  This reduces the surface area for gas exchange.

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