New drugs are extensively tested for toxicity, efficacy and dose.

The idea

Testing a new drug covers three linked questions. Toxicity asks whether the substance harms the body, for example by damaging the liver or kidneys. Efficacy asks whether the drug produces the intended therapeutic effect, such as lowering blood pressure or killing a pathogen. Dose asks what amount gives the desired effect with acceptable side effects, because too little may not work and too much may be toxic. Preclinical laboratory work, often using cells or tissues, can reveal toxicity and suggest a starting dose. Clinical trials then compare groups receiving the drug with controls, using placebos where appropriate, to measure efficacy and refine dose.

For example: A new painkiller might be tested at several doses to find the lowest dose that relieves pain without causing unacceptable side effects.

What earns the marks

• Toxicity testing looks for harmful effects of the drug on the body, including damage to organs or dangerous side effects.
• Efficacy testing shows whether the drug produces the intended therapeutic effect in patients.
• Dose testing finds an amount that gives benefit while keeping side effects at an acceptable level.
• Preclinical laboratory studies can indicate toxicity and help choose a safe starting dose before human trials.
• Clinical trials compare treated groups with controls, often using placebos, to judge efficacy fairly.
• Testing several doses allows the relationship between dose, benefit and harm to be evaluated.

Common mistakes and how to put them right

• Confusing toxicity with efficacy.

  Put it right: Toxicity is about harm, while efficacy is about whether the drug works.

• Treating dose as a single fixed value rather than a range that must be optimised.

  Put it right: Different doses are tested to find one that balances benefit and side effects.

• Assuming a placebo is always used even when an effective treatment exists.

  Put it right: Where a proven treatment exists, it may be unethical to withhold it, so trials may compare the new drug with the existing treatment.

Exam tips

• Define toxicity, efficacy and dose clearly, then link each to a specific stage or purpose of testing.
• Use comparative language when describing trials, such as treated group compared with control group.
• Explain why dose matters by referring to the balance between therapeutic benefit and unwanted effects.