Understanding Clinical Trials

There are two types of clinical trials: interventional and observational. An interventional clinical study tests out an intervention, which could be a drug, device, activity, or procedure. An observational study allows researchers to observe participants during their current (or “usual”) treatment plan. As part of an observational study, outcomes are tracked over time.

When it comes to creating new medicines, clinical trials play an important role. However, several key steps must first take place before a clinical trial can even begin.


It can take years of early laboratory research—known as Discovery and Development—to reveal which drugs demand further study.


Before those drugs can be tested in people, Preclinical Research helps investigators learn about a drug’s basic safety. This helps rule out some potential to cause serious harm. These studies are usually not very large in size and are designed to gather detailed information on a drug’s dosing and potential level of toxicity (potential harmfulness).


Although preclinical research answers important questions about safety, it doesn’t tell us how a drug will affect the human body. This is when Clinical Research comes into play. Clinical research uses trials or studies, which are conducted in human participants.

Clinical trials are carefully planned research studies. Sponsors of clinical trials include companies, universities, or healthcare institutions who initiate and support the research.

In clinical trials, scientists research and evaluate medicines and their effects on healthy people or those who are dealing with a particular condition. The people who participate in clinical trials are dedicated volunteers.

Doctors who are trained in conducting clinical trials are the principal investigators. They carry out the research and interact with study participants. There are other members of the research team that also help to coordinate the trial.

Before each trial begins, there is a strict plan that is established. This plan or protocol includes:

  • What is known about the disease and the medicine in the study
  • Why is the study being conducted and what question(s) will be answered
  • What tests and procedures will be performed
  • The study design and methods to test the questions being asked
  • How often study participants will be examined or evaluated

In addition to clinical studies, observational studies may also take place to help investigators observe and evaluate a specific question or health outcome in human participants. Participants may receive medical products such as drugs, devices, or procedures as part of their routine medical care. However, the participants are not assigned to specific interventions by the investigator (as in a clinical trial).

clinical trial participants are evaluated to see the effects the medication has on their disease and body

Clinical trials take place in phases. Each one serves a different purpose and helps researchers answer very specific questions. The amount of time and the number of people involved changes in each phase to ensure that the medicine in development is safe and effective and that the research can continue. Regulatory authorities must approve each phase before the next one can begin.

Phase 1 trials:
  • Evaluate safety issues, including dosage range, side effects, and how the drug in development works in the body
  • Usually take several months to complete
  • Usually include only a small group of people (fewer than 100)

Approximately 70% of drugs in a phase 1 trial will move on to the next phase.

Phase 2 trials:
  • Further evaluate safety
  • Look at a drug’s effectiveness
  • Usually take several months to several years to complete
  • May include several hundred volunteers (or participants)
  • Usually include study participants who already have the disease or condition for which the drug is being developed

About 33% of drugs studied in a phase 2 trial will move on to the next phase.

Phase 3 trials:
  • Are used to help confirm how well a drug works and to monitor side effects
  • Provide the majority of a drug’s safety data
  • Usually take years to complete
  • May involve up to 3000 participants

Between 25% and 30% of drugs move from phase 3 trials to the next phase.

Phase 4 trials:
  • Occur after a medicine is approved by regulatory authorities and is available for patients
  • Are used by researchers to monitor a drug or treatment’s risks and benefits, as well as the optimal way to use it