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Aspirin originally comes from willow bark, whose active ingredient salicin is converted by the body to salicylic acid. Free notes and 14 questions answered.
Sources of medicines and their discovery is part of Communicable diseases in GCSE AQA Higher Biology.
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Aspirin originally comes from willow bark, whose active ingredient salicin is converted by the body to salicylic acid. Free notes and 14 questions answered.
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Use this lesson to stay inside Communicable diseases while connecting the detail back to the wider Infection and response topic.
Read the core explanations from Sources of medicines and their discovery before testing yourself from memory.
Your medicine cabinet contains drugs that started life in a foxglove flower, willow bark, and mouldy bread. For thousands of years, humans discovered medicines by trial and error from the natural world around them.
This journey from plant to pill reveals how scientific breakthroughs often happen by accident. The story of modern medicine begins not in sterile laboratories, but in gardens, forests, and even contaminated petri dishes.
Digitalis is a powerful heart medicine that comes from foxgloves - beautiful purple flowers that are actually highly poisonous. This drug strengthens the heartbeat and helps treat heart failure.
The discovery happened in 1785 when physician William Withering noticed that patients with heart problems improved after drinking tea made from foxglove leaves. He spent years working out the correct dose - too little had no effect, too much was fatal.
Aspirin, one of the world's most common painkillers, originates from willow bark. Ancient civilizations chewed willow bark to relieve pain and fever, not knowing they were using nature's own aspirin.
The active ingredient is salicin, which the body converts to salicylic acid. However, this natural form caused severe stomach problems. In 1897, chemist Felix Hoffmann modified the molecule to create acetylsalicylic acid - what we now call aspirin.
This shows how modern drug development works: start with a natural product, identify the active ingredient, then modify it chemically to make it safer and more effective.
Penicillin, the first true antibiotic, was discovered by Alexander Fleming in 1928 through a fortunate accident. Fleming left bacterial cultures uncovered in his laboratory over the weekend.
When he returned, he found that mould had contaminated one of his petri dishes. Instead of throwing it away, Fleming noticed something remarkable: the bacteria around the mould had died. The mould was Penicillium, and it was producing a substance that killed bacteria.
Worked example: Fleming's Discovery Process
How did Fleming turn a contaminated culture into a life-saving medicine?
Answer: Fleming's careful observation and scientific method turned an accident into the discovery of antibiotics.
Penicillin revolutionised medicine and has saved millions of lives. It works by preventing bacteria from building their cell walls, causing them to burst and die.
Traditionally, drugs were extracted directly from plants and microorganisms. People learned through generations of trial and error which plants could treat different conditions.
Today, most new drugs are synthesised by chemists in pharmaceutical laboratories. However, the starting point is often still a chemical extracted from a plant. Scientists identify the active ingredient, then modify its structure to make it more effective, safer, or easier to manufacture.
This approach combines the best of both worlds: nature's chemical diversity provides the inspiration, while modern chemistry provides the tools to improve on nature's designs.
Plants have evolved complex chemical defences over millions of years. These compounds, designed to protect plants from diseases and predators, often have powerful effects on human biology too.
Rainforests contain thousands of plant species that haven't been studied yet. Scientists estimate that many future medicines are waiting to be discovered in these natural chemical libraries.
Exam questions often ask you to describe the origins of specific medicines or explain why natural products remain important in drug discovery.
Common mistake: Students often think modern medicines are completely artificial. In reality, many are based on natural compounds that have been chemically modified to improve their properties.
Published by Revise Right. Use the official specification reference to check the requirements for your course. Content updated: 2026-03-20.
Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.
Aspirin originally comes from willow bark, whose active ingredient salicin is converted by the body to salicylic acid. Because this natural form caused severe stomach problems, chemist Felix Hoffmann modified the molecule in 1897 to create acetylsalicylic acid, now synthetically produced as aspirin.
Digitalis comes from foxglove plants and is a heart medication that increases the strength of heart contractions to treat heart failure. In 1785 physician William Withering noticed heart patients improved after drinking foxglove leaf tea, and he spent years working out the correct dose.
Alexander Fleming discovered penicillin in 1928 after leaving bacterial cultures uncovered over the weekend. Mould had contaminated one petri dish, and he noticed the bacteria around it had died. The mould was Penicillium, producing a substance he named penicillin, which kills bacteria by preventing them from building cell walls.
Digitalis is a heart medicine used to treat heart failure: it strengthens the heartbeat by increasing the strength of heart contractions. It is extracted from foxglove plants, which are beautiful purple flowers that are actually highly poisonous.
Aspirin was created in 1897 by chemist Felix Hoffmann, who modified salicylic acid from willow bark to make acetylsalicylic acid. Long before that, ancient civilizations chewed willow bark to relieve pain and fever.
Penicillin was an important discovery because it was the first true antibiotic, and it revolutionised medicine and has saved millions of lives. Alexander Fleming discovered it in 1928 from Penicillium mould; it kills bacteria by preventing them from building their cell walls.
Digitalis was discovered in 1785 by physician William Withering, who noticed that patients with heart problems improved after drinking tea made from foxglove leaves. He spent years working out the correct dose, because too little had no effect and too much was fatal.
Most new drugs are now synthesised by chemists in pharmaceutical laboratories, but the starting point is often a chemical extracted from a plant. Scientists identify the active ingredient, then modify its structure to make it more effective, safer or easier to manufacture, as happened with aspirin.
Plants remain important sources of medicines because they have evolved complex chemical defences over millions of years, and these compounds often have powerful effects on human biology too. Rainforests contain thousands of plant species that have not been studied yet, so many future medicines may be waiting there.
The active ingredient in willow bark is salicin, which the body converts to salicylic acid. This natural form caused severe stomach problems, so in 1897 chemist Felix Hoffmann modified the molecule to create acetylsalicylic acid, which is aspirin.
Modern medicines are not completely artificial. Most new drugs are synthesised by chemists, but the starting point is often a chemical extracted from a plant, which is identified and then chemically modified to make it more effective, safer or easier to manufacture.
In the past, medicines were discovered by trial and error from the natural world, with drugs extracted directly from plants and microorganisms. People learned over generations which plants could treat different conditions, such as foxgloves for heart problems and willow bark for pain.
Penicillin comes from Penicillium mould. Fleming found that this mould had contaminated one of his petri dishes and that the bacteria around it had died, because the mould was producing a substance that killed bacteria.
Rainforests may contain future medicines because they hold thousands of plant species that have not been studied yet. Plants have evolved complex chemical defences over millions of years, and these compounds often have powerful effects on human biology.