Question: How do medicines help with illness and pains? How does the body react to the medicine?

Angela Stokes answered on 8 Nov 2014:

Hi Kizza
Great question. This is a branch of science called pharmacology and it is all about what a medicine does to the body and what the body does to the medicine. It is a very complicated science because all medicines work slightly differently because they act on different chemical signals given out by your body. So for example, a rapidly dividing cancer cell will give out a different signal to a damaged cell near a twisted ankle, which releases a prostaglandin to which your nerve cells are very sensitive and so will make you feel pain. In addition cancer cells can be very different from each other and give out different signals. In some ways this is helpful as we can then make different medicines to act on each different signal so we can ‘target’ a medicine to a particular disease or type of cancer.

The life of a medicine has four distinct stages which we abbreviate to ADME which stands for Absorption, Distribution, Metabolism and Elimination. I will demonstrate these stages for you using the example of paracetamol which as you are aware is a painkiller.

So we will start with absorption. Usually we would swallow a paracetamol either as a tablet or dissolved in water, but we can also rub in a cream containing paracetamol into a sore knee for example, or in a hospital, paracetamol can be given intravenously, through tube connected to a needle placed in a your arm. When we rub in or give paracetamol intravenously the drug is absorbed into the blood stream directly, when taken orally as a tablet or solution it is transported via a blood vessel directly to the liver where some of its power maybe lost (for paracetamol 10-30% of the power can be lost, but it can be a much bigger problem for some other medicines – we call this first pass metabolism). Once the first pass metabolism has occurred the drug is in the blood stream and absorption is complete.

So the drug is now in the blood stream from where it is carried around (distributed) to all parts of the body. When it reaches the liver it is broken down (metabolized) into other chemicals called metabolites by breaking down some of the bonds in the chemical structure. The metabolites are then carried to the kidneys where they pass into the urine and they leave the body (elimination) in the urine when you use the toilet.

So how does that cure your pain which maybe localised in your ankle or head? Well as we have already said when a part of your body is injured it produces a chemical called a prostaglandin to which your body’s nerve endings are very sensitive. When your nerve endings sense a release of prostaglandin, they send a message to the brain telling it where and how much of the body hurts. Paracetamol works by preventing the injured cells from releasing prostaglandin so as the paracetamol has been distributed all around the body it will get to the cells releasing prostaglandin and stop the release – when the nerve endings stop detecting prostaglandin they stop sending messages to the brain and so the pain stops.

Now not all medicines work in exactly the same way, but they all have to be absorbed and distributed to the point of use and then they all have to be broken down and finally removed from the body.

It is also very important to remember that some medicines have actions which aren’t very good in addition to the action we want. These are called adverse effects and a good example is some anti-allergy drugs which as well as helping with the allergy symptoms can also make you feel very sleepy.

I hope this answers your question. It is a very interesting science subject and new medicines are being discovered all of the time and as I said earlier, they are all slightly different. If you are thinking of this as a career I think you would need to study chemistry and biology to A’level and then either do a degree in pharmacology or find a position in a laboratory where you can learn on the job…..either way I think it is very exciting.