Drug development and clinical trials

What you'll learn

This topic covers how new medicines and drugs are developed, tested for safety and efficacy, and approved for use. You'll understand why rigorous testing is essential, what happens in each stage of drug trials, and how scientists ensure results are valid and reliable. This content appears regularly in AQA GCSE Biology exams, particularly in extended response questions.

Key terms and definitions

Preclinical testing — laboratory testing of drugs on cells, tissues and live animals before use in humans to check for toxicity and efficacy

Clinical trials — research studies that test new drugs or treatments on human volunteers to evaluate safety, dosage and effectiveness

Placebo — a substance that looks like the real drug but contains no active ingredient, used as a control in trials

Double-blind trial — a clinical trial where neither the patients nor the doctors know who receives the real drug or placebo until the study ends

Peer review — the process where other scientists critically evaluate research before publication to check validity and identify errors

Dosage — the amount of drug given and how often it is administered

Efficacy — how well a drug works at treating or preventing a disease

Toxicity — how harmful or poisonous a substance is to living organisms

Core concepts

Why new drugs must be tested

Before any new drug can be prescribed to patients, it must undergo extensive testing. This is essential for several critical reasons:

• Safety: New drugs might cause harmful side effects, allergic reactions or even death. Testing identifies these risks before widespread use.
• Efficacy: A drug must actually work and produce the intended therapeutic effect. Many promising compounds fail because they don't work in real patients.
• Optimal dosage: Too little drug won't work; too much may cause harm. Testing determines the correct amount and frequency.
• Legal requirements: Medicines regulators (like the MHRA in the UK) require comprehensive safety data before approving drugs for sale.

Historical disasters emphasize this need. Thalidomide, prescribed in the 1950s-60s for morning sickness, caused severe birth defects because testing was inadequate. Modern testing protocols exist to prevent such tragedies.

Preclinical testing stages

Before human trials begin, drugs undergo preclinical testing in laboratories. This happens in two main stages:

1. Testing on cells and tissues (in vitro testing)

• Drugs are first tested on human cells and tissues grown in the laboratory
• Scientists observe whether the drug produces the desired effect on target cells
• Initial toxicity screening identifies immediately harmful substances
• This stage is cheaper and faster than animal testing
• Many potential drugs fail at this stage

2. Testing on live animals (in vivo testing)

• Drugs that pass initial screening are tested on at least two different mammal species (often mice and rats, sometimes dogs or monkeys)
• Tests evaluate efficacy, toxicity, and side effects in whole living organisms
• Scientists determine how the drug is absorbed, distributed, metabolized and excreted
• They identify safe dosage ranges and observe effects on different organs
• The law requires animal testing before human trials can begin

Limitations of preclinical testing:

• Animals respond differently to drugs than humans do
• Cell cultures don't replicate the complexity of whole organisms
• Some side effects only appear in humans
• Ethical concerns exist about animal testing, though regulations minimize suffering

Clinical trials on healthy volunteers (Phase I)

Once preclinical tests prove promising, drugs enter human testing. Phase I clinical trials involve small numbers of healthy volunteers:

Key features:

• Usually 20-100 healthy adult volunteers participate
• Volunteers are carefully monitored in controlled medical facilities
• Very low doses are given initially, then gradually increased
• Primary goal is safety — identifying side effects in humans
• Secondary goal is establishing safe dosage range
• This phase typically lasts several months

What scientists measure:

• How the body absorbs, distributes and eliminates the drug
• What side effects occur at different doses
• Maximum tolerated dose
• Whether the drug behaves as predicted from animal studies

If serious side effects emerge, the drug may be abandoned. Approximately 70% of drugs pass Phase I successfully.

Clinical trials on patients (Phase II and III)

Phase II trials:

• Involve 100-300 patients who actually have the disease
• Test whether the drug works effectively against the condition
• Continue monitoring safety and side effects
• Determine optimal therapeutic dose
• Last several months to two years
• About 33% of drugs pass this phase

Phase III trials:

• Large-scale testing on 1,000-3,000 patients
• Compare the new drug against existing treatments or placebos
• Conducted across multiple hospitals or countries
• Provide statistical evidence of efficacy and safety
• Last 1-4 years
• Approximately 25-30% of drugs that enter Phase III are eventually approved

These later phases use specific design features to ensure valid results:

Placebos and control groups

Valid clinical trials require comparison between patients receiving the real drug and control groups. This typically involves placebos:

Why placebos are necessary:

• The placebo effect means patients often improve simply from receiving treatment, even if it contains no medicine
• This psychological effect can be powerful — patients expecting improvement often report reduced symptoms
• Without a placebo control group, scientists cannot determine whether improvements result from the drug or expectations
• Comparing drug effects to placebo effects reveals the true therapeutic benefit

Placebo controls:

• Control group patients receive identical-looking pills or injections containing no active drug
• Treatment group receives the actual drug being tested
• Patients don't know which they're receiving
• If the drug group shows significantly better outcomes than the placebo group, the drug is effective

When placebos cannot be used:

• Ethically, placebos aren't appropriate for serious conditions with existing effective treatments
• In these cases, new drugs are compared against current standard treatments
• For example, a new cancer drug would be compared to existing chemotherapy, not a placebo

Double-blind trials

To eliminate bias, modern clinical trials employ a double-blind design:

How double-blind trials work:

• Neither the patients nor the doctors/researchers know who receives the drug or placebo
• Only the trial coordinators have this information (kept in sealed records)
• Allocation to groups is random

Why this matters:

• Patient bias: If patients know they're receiving the real drug, the placebo effect strengthens; if they know they have the placebo, they may report worse symptoms
• Observer bias: Doctors who know which patients have the real drug might unconsciously rate their outcomes more favorably or pay more attention to them
• Double-blinding ensures any differences between groups result from the drug itself, not expectations or biased assessment

Single-blind alternative:

• Sometimes only patients don't know their group assignment (doctors do know)
• Less rigorous than double-blind but simpler to administer

Peer review and publication

After clinical trials conclude, results undergo peer review before publication:

The peer review process:

1. Researchers write a detailed report of their methods, data and conclusions
2. They submit it to a scientific journal
3. The journal sends it to independent experts in the same field
4. These peer reviewers critically evaluate the research
5. They check for errors, bias, invalid methods or unjustified conclusions
6. Reviewers recommend acceptance, revision or rejection
7. Only after passing peer review is research published

Why peer review matters:

• Prevents flawed or fraudulent research from appearing credible
• Other scientists identify mistakes the original researchers missed
• Ensures methods were appropriate and conclusions justified
• Provides quality control for scientific knowledge
• Published research informs medical practice, so accuracy is critical

Limitations:

• Peer reviewers may miss errors or have their own biases
• The process can delay important findings
• Some poor research still gets published
• Reviewers work unpaid, limiting time they can spend

Worked examples

Example 1: Explain why new drugs are tested on animals before being tested on humans. (3 marks)

Mark scheme answer:

• To test that the drug is safe/not toxic (1 mark)
• To test that the drug works/is efficacious/has the desired effect (1 mark)
• Without harming/risking the lives of humans (1 mark)

Alternative acceptable points:

• To find out about side effects (1 mark)
• To determine appropriate dosage (1 mark)

Example 2: A pharmaceutical company is testing a new painkiller in a clinical trial. Describe how the company should use a placebo in this trial and explain why. (4 marks)

Mark scheme answer:

• Some patients receive the real drug and others receive a placebo that looks identical but contains no active ingredient (1 mark)
• Patients should not know which treatment they are receiving (1 mark)
• To prevent the placebo effect/psychological improvement from believing they're receiving treatment (1 mark)
• So researchers can determine whether improvements are due to the drug itself or patients' expectations (1 mark)

Example 3: Explain the advantages of using a double-blind trial rather than just telling patients they're all receiving real medicine. (4 marks)

Mark scheme answer:

• In a double-blind trial, neither patients nor doctors know who receives the real drug or placebo (1 mark)
• This prevents patient bias/the placebo effect from influencing results (1 mark)
• It also prevents observer/doctor bias where doctors might assess patients differently based on which treatment they know the patient received (1 mark)
• This makes results more valid/reliable/objective (1 mark)

Common error to avoid: Students often describe double-blind as "no one knows" — be specific that patients AND doctors don't know, but trial coordinators do maintain records.

Common mistakes and how to avoid them

• Confusing the order of testing: Remember the sequence: cells/tissues → animals → healthy volunteers → patients. Students often forget the healthy volunteer phase or place animal testing after human trials.

• Thinking placebos are used to "trick" patients: Placebos aren't deceptive — patients give informed consent knowing they might receive a placebo. The purpose is controlling for psychological effects, not deception.

• Saying "double-blind means no one knows": Be precise — the doctors AND patients don't know group assignments, but trial administrators maintain sealed records for safety and analysis.

• Forgetting to explain WHY in exam questions: Questions asking "Explain why drugs are tested on animals" require both what happens AND the reason. Don't just state "to test safety" — add "so humans aren't harmed by toxic substances."

• Confusing efficacy with efficiency: Efficacy means how well a drug works at treating disease. Don't write about speed or cost-effectiveness unless specifically asked.

• Not recognizing when placebos would be unethical: For serious conditions with existing treatments, new drugs are compared to current standard care, not placebos. It would be unethical to give cancer patients sugar pills.

Exam technique for "Drug development and clinical trials"

• Command word "Describe": State facts about what happens without explanation. "Patients are randomly assigned to receive either the drug or placebo" — no need to explain why.

• Command word "Explain": Give reasons and link cause to effect. Use "so that," "this means," or "because" to connect your points. For 3-mark questions, provide three distinct explained points.

• Extended response questions: This topic commonly appears as 6-mark questions requiring detailed, structured answers. Use the levels-marked approach: define terms, describe the process, explain why each stage matters, and show how it ensures valid/safe results.

• Mark allocation guides detail: A 4-mark question needs four distinct points. Don't elaborate one point across multiple sentences — make sure you've covered four separate aspects of your answer.

Quick revision summary

New drugs undergo preclinical testing on cells, tissues and animals to check safety and efficacy before human trials begin. Clinical trials proceed through phases: Phase I tests safety in healthy volunteers; Phases II and III test efficacy in patients. Placebos control for psychological effects, while double-blind trials prevent both patient and observer bias. Random group assignment and large sample sizes ensure valid results. Peer review validates research before publication. This rigorous process protects patients while developing effective new medicines.