Drug Discovery and Development

This lesson covers how new drugs are discovered, developed, and tested before they can be used by patients. You need to understand the stages of drug development, the importance of clinical trials, and the concepts of efficacy, toxicity, and dosage. The development of new medicines is a long, expensive, and rigorous process designed to ensure patient safety.

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Where Do Drugs Come From?

Historically, many drugs were extracted from plants and microorganisms. Modern drugs may be discovered from natural sources or designed in laboratories.

Source	Example Drug	Original Use / Source
Plants	Aspirin	Extracted from willow bark — used for centuries as a painkiller
Plants	Digitalis	Extracted from foxgloves — used to treat heart conditions
Microorganisms	Penicillin	Produced by the Penicillium mould — the first antibiotic
Synthetic (laboratory)	Many modern drugs	Designed using computer modelling and chemistry
Plants	Quinine	Extracted from cinchona tree bark — used to treat malaria

Traditional Medicine

Many traditional remedies have been used for thousands of years. While not all are effective, some have led to the discovery of important modern drugs:

• Willow bark was chewed to relieve pain and fever for centuries before aspirin was developed from its active ingredient (salicylic acid)
• Foxglove was used in folk medicine before digitalis was isolated for treating heart arrhythmias
• Cinchona bark was used by indigenous peoples in South America to treat fever before quinine was identified as an antimalarial

Exam Tip: You do not need to memorise the chemical names of these drugs, but you DO need to know that aspirin comes from willow bark, digitalis comes from foxgloves, and penicillin comes from the Penicillium mould. These are specific facts that appear regularly in exams.

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The Drug Development Pipeline

Developing a new drug from initial discovery to patient use typically takes 10-15 years and costs hundreds of millions of pounds. The process has several critical stages:

graph TD
    A[Discovery: identify potential drug compound] --> B[Pre-clinical testing: laboratory and animal studies]
    B --> C[Phase 1 clinical trial: small group of healthy volunteers]
    C --> D[Phase 2 clinical trial: small group of patients with the disease]
    D --> E[Phase 3 clinical trial: large group of patients]
    E --> F[Regulatory approval: reviewed by authorities e.g. MHRA]
    F --> G[Drug approved for general use]
    G --> H[Phase 4: ongoing monitoring after release]

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Pre-Clinical Testing

Before any drug is tested on humans, it must undergo extensive pre-clinical testing:

Laboratory Testing (In Vitro)

What is tested	How
Efficacy	Does the drug work? Is it effective against the target disease?
Toxicity	Is the drug poisonous? Does it damage cells or tissues?
Dosage	What concentration of the drug is needed to be effective?

Testing is first carried out on cells and tissues grown in the laboratory. This allows scientists to study the drug's effects without putting any living organism at risk.

Animal Testing

Purpose	Detail
Test on a whole living organism	Cells in a dish cannot show effects on organs, the nervous system, or the whole body
Check for side effects	Some side effects only appear in a living organism
Determine safe dosage	Helps identify the correct dose before human trials
Legal requirement	In the UK, all potential medicines must be tested on animals before human trials

Animal testing is controversial. Some people argue it is essential for human safety, while others believe it is unethical to cause suffering to animals. This is a topic you may be asked to evaluate in the exam.

Exam Tip: If asked about the purpose of pre-clinical testing, always mention the three key things being tested: efficacy (does it work?), toxicity (is it harmful?), and dosage (how much is needed?). These three terms are essential.

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Clinical Trials (Testing on Humans)

If a drug passes pre-clinical testing, it moves to clinical trials — testing on human volunteers. Clinical trials are conducted in phases:

Phase 1 — Safety

Feature	Detail
Participants	Small group of healthy volunteers (typically 20-100)
Purpose	Test for side effects and determine a safe dosage
Duration	Several months
Key question	Is the drug safe for humans?

Phase 2 — Efficacy

Feature	Detail
Participants	Small group of patients who have the target disease (typically 100-300)
Purpose	Test whether the drug works (is effective against the disease)
Duration	Several months to two years
Key question	Does the drug treat the disease effectively?

Phase 3 — Large-Scale Testing

Feature	Detail
Participants	Large group of patients (typically 1,000-3,000+)
Purpose	Confirm efficacy and safety on a large scale; compare with existing treatments
Duration	One to four years
Key question	Is the drug better than existing treatments? Are there rare side effects?

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Placebos and Double-Blind Trials

To ensure clinical trial results are valid, scientists use placebos and double-blind methods:

Term	Definition
Placebo	A dummy treatment (e.g. sugar pill) that looks identical to the real drug but contains no active ingredient
Placebo effect	An improvement in symptoms caused by the patient believing they are receiving treatment, not by the drug itself
Single-blind trial	The patient does not know whether they are receiving the drug or the placebo
Double-blind trial	Neither the patient nor the doctor knows who is receiving the drug or placebo — this prevents bias
Peer review	The results of clinical trials are reviewed by independent scientists before publication

Why Use Placebos?

Placebos allow scientists to determine whether any improvement in patients is due to the drug itself or simply due to the placebo effect. Without a placebo group for comparison, it would be impossible to know if the drug truly works.

Why Use Double-Blind Methods?

If the doctor knows which patients are receiving the real drug, they might unconsciously treat those patients differently or interpret results differently. The double-blind method eliminates this bias, making the results more reliable.