What Is a Clinical Trial?

In short: A clinical trial is a planned study in people that evaluates an investigational medicine and generates evidence about its effects, safety or efficacy. The study question and design vary across development, while participant protection and reliable data remain central.

What is a clinical trial?

In India, the New Drugs and Clinical Trials Rules, 2019 define a clinical trial, in relation to a new or investigational new drug, as a systematic study in people that generates data about clinical or pharmacological effects, adverse effects, safety, efficacy or tolerance (Rule 2(j)). The exact regulatory scope depends on the applicable law.

ICH E8(R1) uses the broader term clinical study for research on one or more medicinal products in people at any point in the product lifecycle, before or after marketing authorisation (2021, §1). A study should be designed around a clear research question and generate information suitable for decisions, while protecting participants (ICH E8(R1), §§2.1–2.2).

Clinical studies do not all compare two treatment groups. The design depends on what researchers need to learn, the medicine and the participant population. In India, the NDCTR describes a clinical-trial protocol as a document covering the study background, objectives, design and methods, among other elements (Rule 2(k)).

Typical stages in medicine development

ICH E8(R1) describes common types of studies across development. Phase labels are shorthand for typical objectives; they do not mean every medicine follows one fixed sequence. New information may change the development plan or prompt additional studies (ICH E8(R1), §§2.2, 4.3).

Phase I: initial human pharmacology

Early studies usually examine initial safety and tolerability, how the medicine moves through the body, and its pharmacological effects. They may involve healthy volunteers or a selected patient group, depending on the medicine and the study objective (ICH E8(R1), §4.3.1).

Phase II: exploratory studies

Exploratory studies generally investigate safety and possible benefit in selected patients. They can help refine the dose, treatment schedule, target population and outcomes for later research (ICH E8(R1), §4.3.2).

Phase III: confirmatory studies

Confirmatory studies assess whether earlier evidence supports safety and benefit for the intended use and population. They may provide evidence for marketing authorisation and the information needed for product-use instructions (ICH E8(R1), §4.3.2).

Phase IV: post-approval studies

After approval, additional studies may examine safety, efficacy or use in the approved indication, including in populations or settings that need further study. These are commonly called Phase IV studies (ICH E8(R1), §4.3.4).

Participant protection and study quality

Good Clinical Practice (GCP) sets ethical and scientific expectations for planning, conducting, recording, overseeing, analysing and reporting clinical trials. ICH E6(R3) says trials should protect participants’ rights, safety and well-being and generate reliable results (2025, Principles 1 and 9). Its informed-consent guidance calls for information and a genuine opportunity for participants to decide whether to take part (§2.8).

In India, a person intending to conduct a clinical trial covered by the New Drugs and Clinical Trials Rules must obtain approval from an Ethics Committee registered under Rule 8 (NDCTR 2019, Rule 6). The applicable protocol, ethics review and other permissions depend on the study and current local requirements.

Related reading: important definitions used in clinical trials. For broader pharmaceutical quality-system concepts outside clinical-trial requirements, see ICH Q10 and the pharmaceutical quality system.

Frequently asked questions

Does every clinical study test a new medicine?

No. Clinical research can address different questions over a medicine’s lifecycle. In India, the NDCTR definition of a clinical trial refers to a systematic study of a new or investigational new drug; ICH E8(R1) also covers clinical studies before and after marketing authorisation.

Are all studies divided into four phases?

No. The phases describe typical development objectives. Study plans may vary, stages can overlap, and later information may lead to additional studies.

Are clinical trials always comparisons between treatment groups?

No. Designs vary with the research question, the medicine and the participants. Each study should use a design that can answer its stated objective.

What is the main purpose of GCP?

GCP provides an ethical and scientific framework for trial conduct, with participant protection and reliable results as central aims. Applicable regulatory requirements also govern each study.

References

• International Council for Harmonisation (ICH). E8(R1): General Considerations for Clinical Studies, ICH Consensus Guideline, Step 4, 6 October 2021, §§1–2 and 4.3. Official guideline PDF.
• International Council for Harmonisation (ICH). E6(R3): Good Clinical Practice, ICH Harmonised Guideline, Step 4, 6 January 2025, Principles 1 and 9, §2.8. Official guideline PDF.
• Government of India, Ministry of Health and Family Welfare. New Drugs and Clinical Trials Rules, 2019, G.S.R. 227(E), 19 March 2019, Rules 2(j), 2(k) and 6. Official CDSCO rules PDF.