The discovery of new drugs

Plant extracts

Certain drugs can be extracted from natural sources and have been known about for a long time. For example, willow bark was used by the ancient Greeks to help cure fevers and pains. It was later discovered that the active ingredient was salicylic acid. This was modified by chemists into the substance we call aspirin, which is less irritating to the stomach than salicylic acid. Another example is the heart drug digitalis, which is extracted from foxgloves.

Plants are still important today, but most plant drugs are now created in a laboratory by scientists at pharmaceutical companies. These companies now have synthetic versions of the plant extracts and use these as the starting point to develop new drugs.

New medical drugs have to be tested to ensure that they work and are safe, before they can be prescribed. Drugs are tested for:


This is important as some drugs are toxic and have other side effects that might be harmful to people


This is also known as efficacy and checks how well the drug cures the disease, or improves symptoms.


This varies and has to closely controlled, as too high a concentration might be toxic.

Three stages of testing drugs

There are three main stages of testing:

  1. Pre-clinical testing
    • The drugs are tested using computer models and human cells grown in the laboratory. Many substances fail this test because they damage cells or do not seem to work.
  2. Pre-clinical animal testing
    • Drugs that pass the first stage are tested on animals. In the UK new medicines have to undergo these tests. But it is illegal to test cosmetics and tobacco products on animals. A typical test involves giving a known amount of the substance to the animals, then monitoring them carefully for any side-effects.
  3. Clinical testing
    • Drugs that have passed animal tests are used in clinical trials. They are tested on healthy volunteers to check that they are safe. The substances are then tested on people with the illness to ensure that they are safe and that they work.

During clinical trials it needs to be determined if the drug is more effective than current treatments. This may involve asking the patient if they feel better or not. To avoid bias a number of strategies are applied:

  • clinical trials often involve one group who are given the drug which is being tested and a control group who are given a placebo
  • blind trials - In this trial the patients are not told if they are in the trial group or the placebo/control group
  • double blind trials - In this trial neither the patient nor the doctor administering the drug knows if the patient is receiving the drug or a placebo in an attempt to eliminate bias altogether

Some people consider drug trials to be dangerous, so how safe are they? Everything comes with a level of risk.

Placebos are also used to ensure that the drug is having an effect and that any changes are not due the experimental trial process.

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