Drug Discovery and Development

This lesson covers how new drugs are discovered, developed, and tested before they can be used to treat patients. It also looks at the sources of drugs — including those derived from plants and microorganisms. This is required knowledge for the AQA GCSE Combined Science Trilogy specification (8464).

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Where Do Drugs Come From?

Many drugs have been discovered from natural sources — plants, microorganisms, and other living organisms:

Drug	Source	Use
Aspirin	Originally extracted from willow bark (contains salicin)	Pain relief and anti-inflammatory
Digitalis	Extracted from foxglove plants	Treats heart conditions
Penicillin	Discovered from the mould Penicillium	Antibiotic — kills bacteria
Quinine	Extracted from cinchona tree bark	Antimalarial drug

Exam Tip: You need to know that aspirin was developed from a chemical found in willow bark and that digitalis comes from foxgloves. These are classic exam examples of drugs from natural sources.

Today, most new drugs are synthesised by chemists in laboratories. However, the starting point is often a compound discovered in nature.

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The Drug Development Process

Before any new drug can be prescribed to patients, it must go through a rigorous testing process. This typically takes 10–15 years and costs hundreds of millions of pounds.

Stage 1: Discovery and Pre-Clinical Testing

Step	What Happens
Identify a target	Scientists identify a molecule or process in the body that could be targeted to treat a disease
Discover a lead compound	A chemical compound is found (from nature or synthesised) that may affect the target
Laboratory testing	The compound is tested on cells and tissues in the lab to check it has an effect
Animal testing	The drug is tested on live animals to check for toxicity (is it poisonous?), efficacy (does it work?), and to find the correct dosage

Exam Tip: Pre-clinical testing involves testing on cells, tissues, and animals before any testing on humans. The purpose is to check the drug is safe and effective.

Stage 2: Clinical Trials (Testing on Humans)

Clinical trials involve testing the drug on human volunteers in a carefully controlled process:

Phase	Purpose	Participants
Phase 1	Test for safety and side effects; find the correct dosage	Small number of healthy volunteers
Phase 2	Test for efficacy (does it work?) and further check safety	Small number of patients with the disease
Phase 3	Large-scale testing to confirm efficacy and monitor side effects	Large number of patients (hundreds or thousands)

graph TD
    A[Discovery — identify lead compound] --> B[Pre-clinical: lab testing on cells/tissues]
    B --> C[Pre-clinical: animal testing — toxicity, efficacy, dosage]
    C --> D[Phase 1 clinical trial — healthy volunteers — safety and dosage]
    D --> E[Phase 2 clinical trial — patients — does it work?]
    E --> F[Phase 3 clinical trial — large-scale — confirm efficacy]
    F --> G[Regulatory approval — drug licensed for use]
    G --> H[Phase 4 — ongoing monitoring after release]

Stage 3: Regulatory Approval and Monitoring

Step	Detail
Regulatory review	An independent body (e.g. MHRA in the UK) reviews all the evidence and decides whether the drug is safe and effective enough to be licensed
Ongoing monitoring (Phase 4)	After the drug is approved, it continues to be monitored for any long-term or rare side effects

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Placebos and Double-Blind Trials

To ensure clinical trial results are reliable, 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	The phenomenon where patients feel better simply because they believe they are receiving treatment
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 the placebo — this is revealed only after the trial

Why Use Placebos?

Reason	Explanation
Control for the placebo effect	Some patients improve simply because they think they are being treated — the placebo group accounts for this
Isolate the drug's effect	By comparing the drug group with the placebo group, scientists can determine whether any improvement is due to the drug itself
Reduce bias	In a double-blind trial, neither patient nor doctor can unconsciously influence the results

Exam Tip: If asked "Why are double-blind trials used?", say: "To prevent bias — neither the patient nor the doctor knows who receives the drug, so their expectations cannot influence the results."

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Peer Review

After clinical trials, the results are published in scientific journals and undergo peer review:

Feature	Detail
What is peer review?	Other independent scientists critically evaluate the research methods, data, and conclusions
Why is it important?	It checks the results are valid, reliable, and not influenced by bias or error
What happens if issues are found?	The paper may be revised, rejected, or retracted

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Why Does Drug Development Take So Long?

Reason	Explanation
Safety	Multiple stages of testing ensure the drug does not cause harmful side effects
Efficacy	The drug must be proven to work better than existing treatments or a placebo
Dosage	The correct dose must be established — too little may be ineffective; too much may be toxic
Regulations	Strict rules govern each stage of testing to protect patients
Scale	Phase 3 trials require thousands of participants and take years

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Ethical Considerations

Issue	Discussion
Animal testing	Necessary to check for toxicity before human trials, but raises ethical concerns about animal welfare
Placebo use	Is it ethical to give some patients a placebo instead of a potentially life-saving drug? In some trials, placebos are compared against existing treatments rather than no treatment
Informed consent	All human volunteers must be fully informed about the trial and give consent
Access to new drugs	New drugs are often expensive — should everyone have equal access?

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Common Mistakes

Mistake	Correction
"Drugs are only tested on animals"	Drugs are tested on cells, tissues, animals, and humans in clinical trials
"Placebos are used to trick patients"	Placebos are used to control the experiment and ensure any observed effect is due to the drug, not the patient's belief
"Double-blind means the patient is blindfolded"	"Blind" means the participant does not know which treatment they are receiving — it has nothing to do with sight
"Drugs go straight from animal testing to being sold"	There are three phases of human clinical trials plus regulatory approval before a drug can be prescribed
"Aspirin is a synthetic drug"	Aspirin was originally derived from a compound in willow bark (a natural source)

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Summary