Types of Clinical Trials

There are many different kinds of clinical trials that can vary by objective, design, and number of participants, as well as other factors.

Different types of clinical studies can be categorized by purpose, which vary in both design and goals, depending on what researchers are trying to find out. Clinical trials can also be broken down by phases, ranging from preclinical to post-marketing, depending on what stage of the research process a particular treatment or intervention is in at a given time.

Here’s a breakdown of each type of clinical trial and what’s involved.

Types of clinical trials by purpose

Not all studies are created with the same purpose. Some may be designed to understand the impact and effects of a new medical device, while others may be aimed at evaluating the effectiveness or safety of an investigational drug. Still others may focus on understanding a particular condition, how genetics may play a role in disease risk, or factors that affect quality of life.

Here are some of the most common types of studies:

• Interventional or treatment trials: the type of study that is most familiar to people; these studies test treatments not yet approved for use.
• Prevention trials: designed to analyze ways to stop medical conditions from occurring in the first place.
• Observational trials: used to examine health issues in large groups of individuals and do not involve any study intervention.
• Diagnostic and screening trials: designed to help find new ways to detect and diagnose medical problems.
• Genetic trials: intended to examine genetic links and traits in families and how these factors might affect health risks and outcomes.
• Quality of life trials: focused on the comfort of patients and works to minimize the effects of a given condition and its treatments.

Types of clinical trials by phase

There are also different clinical trial phases, which vary by number of participants and specific objectives, depending on where a particular treatment or intervention is at in the research process.

• Preclinical testing: the animal testing phase that takes place in the lab and is required before an intervention can be studied in humans.
• Phase 1 trials: the first research step that includes human volunteers (a small group of about 20 to 80 participants*) and evaluates the safety of a given experimental drug or treatment as well as determining a safe dose range and identifying potential side effects.
• Phase 2 trials: includes larger groups of human volunteers (100 to 300 participants*) to measure the effectiveness of the intervention and to continue to evaluate its safety.
• Phase 3 trials: includes even more participants (1,000 to 3,000 individuals*) to confirm the intervention’s effectiveness, track of potential side effects, compare the treatment with others already in use, and gather data about how the experimental intervention can be safely administered.
• Phase 4 trials: involves a much larger study population (up to thousands of participants*) and helps to gather more information about the long-term safety and efficacy of a treatment after its approval; also known as post-marketing research.

*Numbers may differ relative to the prevalence of the disease and involve a smaller number of participants for rarer conditions.