How Do Clinical Trials Work?

Clinical trials are an important component of medical research.1 They allow teams of researchers to discover whether a new treatment, like a new medication, diet, or medical device, is safe and effective to prevent or treat diseases in humans.

In order for clinical trials to effectively gather information for researchers while mitigating risks to participants, regulators for studies specify a particular process, also called a protocol, which outlines how the study will work. Read on to learn about the broad outlines of a clinical trial protocol and what it means for participants.

The Clinical Trials Process: An Overview

People who volunteer for clinical trials are called study participants.1 Participants can expect the clinical trial process to involve the following steps:

  1. Recruitment: The research team explains the trial in detail to people who are interested while gathering information about them to be sure they qualify to participate.
  2. Informed consent: After would-be participants are presented details of the trial and have all their questions answered by the research team, they sign a form agreeing to participate, if selected.
  3. Screening: The research team assesses each would-be participant to be sure they qualify for the trial. They notify selected participants and explain the next steps in detail.
  4. Baseline visit: Participants have an initial visit with the research team to measure their physical and mental “baseline,” which is participants’ conditions prior to starting the trial.
  5. Random assignment: In many studies, participants are randomly assigned to either the investigational group (that receives the study drug) or the control group (that receives placebo). (For more information on study groups, read our section explaining placebos below.)
  6. Trial phase: Participants follow the steps laid out in the trial protocol, taking care to report any issues or concerns to the research team along the way.
  7. Data collection: Participants visit the research site at regular intervals to meet with the team for evaluations and discussions about the trial. The researchers collect information about the effects of the intervention and participants’ safety and well-being.

Throughout the clinical trial, participants are encouraged to continue seeing their regular physician for routine healthcare needs that are not related to the study.

How Does Treatment Differ in a Clinical Trial?

The main difference between a clinical trial and the medical treatment a patient receives in their doctor’s office or at a hospital is that the clinical trial follows a specific protocol that answers specific research questions while striving to ensure the safety of study participants.2 The clinical trial protocol outlines everything that participants will be expected to do, as well as what participants can expect from the research team. Protocols also contain detailed explanations of the risks and benefits of participating in clinical trials.

How Long Do Clinical Trials Take?

Clinical trials that test treatments on human participants involve four phases.3 The clinical trial timelines for Phases 1-3 will depend on which phase is being conducted. Phase 4 is an ongoing process, so timelines are not clearly defined.

  • Phase 1: Researchers enroll a small group of healthy participants who meet the trial criteria to test the safety of a new drug or device in humans. This process usually takes several months to complete.
  • Phase 2: The research team continues to monitor the safety of the drug or device, carefully noting the frequency and severity of any side effects that emerge. They also begin looking at the efficacy (the ability to produce a desired or intended result) of the This phase studies the intervention on a new set of selected participants, all of whom are affected by the medical condition being studied. The size of this group depends on what is needed to achieve statistical significance in the analysis, which could be hundreds or several thousands of participants. This phase may typically last up to 2 years.
  • Phase 3: This phase closely examines the safety and efficacy of the new drug or device in participants to make the best determination of the appropriate dose and its impact upon the general population. The data from Phase 3 trials is submitted to the FDA for approval. This phase may typically take 1 to 4 years but is sometimes combined with Phase 2.
  • Phase 4: After a new drug or device receives FDA approval, the manufacturer may have researchers continue to monitor its safety and efficacy to see if any new findings emerge. Because this phase occurs after a medical intervention has received approval to be marketed to the public, many more individuals may be included in this phase. Any findings are promptly reported to regulatory agencies and medical professionals to better guide the use of the product in patient care settings.

What Is a Placebo and Why Are Placebos Used in Clinical Trials?

A placebo is a product made to look like a medication, but with no active ingredient in it. In many research studies, it is important for participants to be unaware of whether they are receiving the actual treatment during the study. Placebos are used in clinical trials to more accurately measure the impact of the actual medication.

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How exactly does placebo use fit into a research study? Before agreeing to participate in the trial, all prospective study participants are asked to provide informed consent. This involves explaining all relevant information about how the trial will work, including the fact that they may receive either active treatment or a placebo. In the many studies that use randomized groups, the study participants who receive the actual medication are in the “investigational group,” while participants who receive the placebo are in the “control group.”

Not all clinical trials involve a control group using placebos. If using a placebo might put participants at risk by preventing them from receiving an effective therapy (for instance, in many trials of cancer therapies), placebos are prohibited. In certain other clinical trials, participants who receive the placebo in the first part of a study can be switched to receiving the actual medication for a later phase in the trial, to see what impact, if any, is observed.4

What Is Random Assignment in Clinical Studies?

Random assignment is the process by which study participants are selected for inclusion in a particular group in a clinical trial. For a clinical trial to be scientifically valid, the researchers must rule out any alternative explanations of their results and provide meaningful explanations for why and how they achieved their predicted outcomes.5 Special computer programs can randomly assign participants to investigational or control groups in relatively equal numbers of a specified age, gender, and other factors to minimize the impact of such factors on trial results.

Even with the best random assignment process, study participants may be dissatisfied with the group to which they are randomly assigned.5 This may lead to their refusal to participate or to withdraw from the trial before its completion. For this reason, the research team may ask participants to share their feelings about the proposed treatment before accepting them into the trial.

Random assignment benefits the clinical trial in several ways.6 It eliminates selection bias, where treatments are preferentially given to certain participants and not to others. Random assignment allows researchers to compare the study groups and apply statistical methods to evaluate the treatment effect in a scientifically meaningful way. It also facilitates “blinding” of the participants, the researchers, or both, depending on how the trial is designed.

What Does Blinding Mean?

Blinding is the process of intentionally withholding information from one or more parties involved in a clinical trial to prevent anyone from influencing the results.7 Specifically, blinding means that the study participants don’t know if they are receiving the actual treatment and or the placebo.

Depending on the study design, any or all of the following groups may be blinded:

  • Study participants
  • Medical staff providing treatment
  • The physician who evaluates the treatment effectiveness
  • The research team that analyzes the trial results

In “single-blinded” studies, only the participants are blinded.7 The best designed trials are “double-blinded,” where the participants, medical staff, evaluating physician, and research analysts are all unaware of who is receiving the actual treatment during the study.

Blinding is an essential step in eliminating bias that may otherwise affect the outcome of a scientific study.7 It is a core design component of sound clinical trials.

In the event of an emergency, the blind can be broken at any time in the study in order to provide care for the participant. For example, if a participant has a clinical event where the treating medical provider would need to know if the subject received a placebo or the investigational agent, the researchers can “break the blind” in order to obtain the information needed to treat the individual.