What is a clinical trial?

Clinical trials are an extremely important stage of the research and development process. In controlled and regulated environments, they are the primary way that doctors and researchers find out if an intervention like a new drug, diet or medical device is safe and effective in people.


72% of survey participants agree that clinical trials provide patients with access to potential treatments not otherwise available.

Who runs clinical trials?

There has been a significant increase in clinical trial activity in recent years. As of February 2021, 366,000 active clinical studies were registered globally.

A clinical trial can be run by a pharmaceutical company, hospital group or research institution and often with the support of a clinical research organisation.

Type of clinical trials

There are many different types of clinical trials.

Interventional trials aim to manage, prevent or treat a condition or disease. Examples include drug compounds, gene innovations, cell-based approaches, devices, surgical techniques, delivery systems and diet, to name but a few. At this stage, we use the word “intervention” instead of the word “treatment”. This is because these approaches are still being studied for safety and efficacy and are not yet established or recognised therapies.

Diagnostic trials are conducted to find better ways (e.g. tests, imaging, screening) for earlier diagnosis of a disease or condition.

Observational trials can include Natural History Studies which monitor progression of disease over a period of time to further understand how a condition develops, its severity and identify potential therapeutic windows.


Clinical trials are designed to answer specific research questions and safeguard the health of participants so they can often have very strict eligibility criteria with specific inclusion and exclusion factors. This means only certain individuals can participate. One’s age, genetic profile, stage of disease and medical history are all factors in determining eligibility for a study.


Despite being an important step, many clinical trials experience significant delays or difficulties in recruiting enough study participants. This is particularly the case for rare diseases where prevalence of a condition may be low. Often patients don’t know where to find or access a trial suitable for them. In turn, medical specialists may only be aware of trials taking place within their own geographical region or hospital.

There are many ways that people can find about clinical trials taking place that may be of relevance to them. This could be through their healthcare provider, patient advocacy organisations, online groups or forums, patient registries, online databases or by contacting trial sponsors directly. If they meet the eligibility criteria for a specific trial, they can then be recruited by their doctor, a clinical research organisation or clinical trial staff.

Participation in a clinical trial may require a significant time and commitment on the part of the individual and family. As such, people may drop out during the study which means that retention of study participants in a clinical trial is also a challenge.

Clinical Trial Phases:

We can think of a clinical trial as a racehorse on the day of a big race. Each racehorse will have to jump a number of fences successfully before reaching the finish line. Similarly, each clinical trial will have to pass a number of hurdles, or phases, before it can be used in clinical practice. The earlier phases of a clinical trial test how safe the intervention is, while latter stages test how effective it is. Each phase must be completed before moving on to the next.

  • Phase I

    A Phase I study is focused on safety, ensuring that the potential intervention does no harm or results in any dangerous side effects. They are usually small trials, recruiting less than thirty patients. For rare diseases, the number of participants can be even smaller. Investigators may also test increasing doses of a treatment in different patient groups, often referred to as dose escalation, to identify the maximum tolerable level.

  • Phase II

    A Phase II study retains the major focus on safety but also begins to evaluate efficacy in a larger number of individuals. For rare diseases, this may still be a small group of participants. In some cases, the intervention may be compared against a treatment currently in use. In other cases, it may be tested against a non-functional intervention (known as a placebo or “sham” treatment). A phase II is likely to take two to four years.

  • Phase III

    A Phase III study is the final, or “pivotal,” stage before seeking regulatory and marketing approval from the U.S. Food and Drug Administration (FDA) or the European Medicines Agency (EMA). In this phase, investigators are looking for strong evidence of efficacy. The therapy may be studied at multiple clinical sites in different regions and countries to determine if investigators can achieve the same results independently.

  • Combined Phases

    For many emerging therapies targeting rare conditions, phases are combined. For example, Phase I and II can be combined as a Phase I/II, or Phase II and III as a Phase II/III. This is done to save time and money but also to accommodate the limited number of participants available for the clinical trial.

  • Phase Four (IV)

    Phase Four studies are performed after an intervention has been clearly shown to be safe and effective and has been granted approval in a country. They are performed to understand more about the treatment in a wider population over a longer timeframe and in a real-world setting.

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