Clinical Trials: How Medical Research Studies Work
Author: Disabled World (DW)
Updated/Revised Date: 4 Aug 2026
Table of Contents:
Synopsis - Definition - About This Section - FAQs - Publications - Subtopics
Synopsis
Understand what clinical trials are, how they test new treatments in people, the four drug development phases, and the five NIH trial types explained clearly.
At a Glance
- 1 - The NIH organizes clinical trials into five distinct types.
- 2 - Phase IV studies take place after a drug has already been approved.
- 3 - Compassionate use trials can offer experimental therapies before final FDA approval.
- 4 - A trial can only begin once Health Authority or Ethics Committee approval is granted in that country.
Topic Definition
- Clinical Trials
Clinical trials are research studies carried out in people to find out how well new medical approaches work and whether they are safe. Each study is built around specific scientific questions and looks for better ways to prevent, screen for, diagnose, or treat a disease, sometimes comparing a new treatment against one that is already in use. These prospective biomedical or behavioral studies test interventions such as vaccines, drugs, dietary supplements, and medical devices, along with known treatments that merit further study. During a trial, investigators recruit participants who meet set criteria, provide the treatment, and gather health data over a defined period, which the sponsor then analyzes using statistical methods. In the United States, drug trials generally move through four phases, and only after successfully passing the earlier phases is a treatment usually approved for the wider population.
Overview
Clinical trials are defined as research studies that test how well new medical approaches work in people. Each study answers scientific questions and tries to find better ways to prevent, screen for, diagnose, or treat a disease. Clinical trials may also compare a new treatment to a treatment that is already available. Such prospective biomedical or behavioral research studies on human participants are designed to answer specific questions about biomedical or behavioral interventions, including new treatments (such as novel vaccines, drugs, dietary choices, dietary supplements, and medical devices) and known interventions that warrant further study and comparison.
Clinical trials are conducted to allow safety and efficacy data to be collected for new drugs or devices. These trials can only take place once satisfactory information has been gathered on the quality of the non-clinical safety, and Health Authority/Ethics Committee approval is granted in the country where the trial is taking place.
During the clinical trial, the investigators: recruit patients with the predetermined characteristics, administer the treatment(s), and collect data on the patients' health for a defined period. These data include measurements like vital signs, amount of study drug in the blood, and whether the patient's health gets better or not. The researchers send the data to the trial sponsor, who then analyzes the pooled data using statistical tests.
The U.S. National Institutes of Health (NIH) organizes trials into five different types:
- Prevention trials: look for better ways to prevent disease in people who have never had the disease, or to prevent a disease from returning. These approaches may include medicines, vitamins, vaccines, minerals, or lifestyle changes.
- Screening trials: test the best way to detect certain diseases or health conditions. Diagnostic trials: conducted to find better tests or procedures for diagnosing a particular disease or condition.
- Treatment trials: test experimental treatments, new combinations of drugs, or new approaches to surgery or radiation therapy.
- Quality of life trials: explore ways to improve comfort and the quality of life for individuals with a chronic illness (a.k.a. Supportive Care trials).
- Compassionate use trials: provide experimental therapeutics before final FDA approval to patients whose options with other remedies have been unsuccessful. Usually, case by case approval must be granted by the FDA for such exceptions.
Clinical trials used in drug development are sometimes described by phase. In the U.S. these phases are defined by the Food and Drug Administration (FDA). Clinical trials involving new drugs are commonly classified into four phases:
- Each phase of the drug approval process is treated as a separate clinical trial.
- The drug-development process will normally proceed through all four phases over many years.
- If the drug successfully passes through Phases I, II, and III, it will usually be approved by the national regulatory authority for use in the general population.
- Phase IV are 'post-approval' studies.
Frequently Asked Questions
Are clinical trial participants paid to take part
Compensation varies by study, with some trials offering payment or reimbursement for time and travel while others provide no payment at all, so participants should ask before enrolling.
Is it safe to volunteer for a clinical trial
Trials follow strict safety rules and require ethics approval before starting, though some risk remains because the treatments being studied are still experimental.
Can a participant leave a clinical trial early
Yes, taking part is voluntary and a participant can withdraw at any time and for any reason without losing access to their regular medical care.
What is informed consent in a clinical trial
Informed consent is the process of explaining a study's purpose, risks, and benefits to volunteers so they can decide freely whether to take part before enrolling.
Who pays for a clinical trial
Clinical trials are funded by sponsors such as government agencies, universities, hospitals, and pharmaceutical or medical device companies that develop the treatment being tested.
What is a placebo in a clinical trial
A placebo is an inactive substance made to look like the treatment being tested, used so researchers can compare its effects against the real intervention.
How do people find clinical trials to join
People can find trials through their doctor, hospital research centers, and public registries that list studies along with their locations and eligibility requirements.
Curated and edited by Ian C. Langtree, Founder & Editor-in-Chief, Disabled World. This section is maintained by the Disabled World editorial team.
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