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.


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.

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.

Tobacco and Smoking

Cigarettes are harmful in three ways, they contain:

  • 1.Nicotine – addictive drug that leads to heart disease. Nicotine raises blood pressure and narrows arteries
  • 2. Tar – coats the lining of the lungs > less O2 is absorbed. Tar contains carcinogens which cause cancers
  • 3. Carbon monoxide – poisonous gas which joins onto red blood cells making them incapable of transporting oxygen around the body

Parkinson’s disease and smoking – is it worth the risk?

Parkinson’s disease is a disorder of the central nervous system that is caused by a loss of cells in an area of the brain. Those cells produce dopamine, a chemical messenger responsible for transmitting signals across synapses. Loss of dopamine causes some nerve cells to fire out of control, leaving patients unable to control their movement in a normal way.

Patients often start off with slight shaking of the hands and they may eventually have difficulty walking, talking or completing other simple tasks. The disease can be treated by giving a drug called L-dopa. The brain uses this chemical to make more dopamine. Unfortunately, the drug has a number of side effects and larger doses of the drug are often needed as the disease gets worse.

Patients therefore have a difficult decision to make. In recent studies on Parkinson’s disease it has been suggested that there is a correlation between smoking and a reduced risk of having the disease. Doctors are trying to find out if this means that smoking actually causes the protection.

Do these results mean that doctors are actually advising patients to smoke? No, they are not. As a doctor said:

“The dangers of cigarette smoking far outweigh any as yet inconclusive evidence that there are advantages of protection from Parkinson's disease. You need to look at the risks – smoking is the largest single cause of preventable death in many countries. About 1 in 1000 people are likely to get Parkinson’s disease but every year over 100 000 people die through cigarette smoking in the UK. Smoking is just not worth the risk.”


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.

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. 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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