What Is the Difference Between Pragmatic and Explanatory Clinical Trials?

Imagine two studies testing the same new asthma medication. In the first, researchers pick 200 patients who have asthma and nothing else, watch them closely for a year in a specialized clinic, and check that every patient takes every dose on time. The medication works well. In the second study, researchers test the same medication in regular family doctors' offices, with thousands of patients who also have heart conditions, diabetes, or other health issues, and who use the inhaler however they normally would. The medication still helps, but the benefit is smaller and the results are less tidy.

Both studies are accurate. They were just answering different questions. The first asked whether the medication can work under perfect conditions. The second asked whether it does work in everyday life. That is the basic difference between pragmatic and explanatory clinical trials, and understanding it helps make sense of how new treatments are tested before they reach patients.

The Two Questions a Clinical Trial Can Answer

Most clinical trials are trying to answer one of two questions. The first is the "can it work" question. Researchers want to know if a new treatment can produce a clear benefit when conditions are as good as they can possibly be. They pick patients who fit a narrow profile, follow a strict schedule, and track results carefully. This is what an explanatory trial does.

The second is the "does it work" question. Here, researchers want to know if the treatment actually helps people in normal life, where things are messier. Patients have other health problems, miss doses sometimes, see different doctors, and just live their lives. This is what a pragmatic trial does. To learn more about how clinical trials work in general, see Clinical Trials Explained: Simple Guide for Beginners.

A useful way to picture the difference is to think of testing a recipe. An explanatory trial is like making the dish in a professional kitchen, with exactly the right ingredients measured to the gram, by a chef who has cooked it a hundred times. A pragmatic trial is like seeing how the same recipe turns out when home cooks make it from a printout, with whatever they have in the cupboard. Both tests tell you something useful, and the answers are usually different.

The idea of separating these two questions was first proposed in 1967 by two French researchers, Schwartz and Lellouch. The terms they came up with, explanatory and pragmatic, are still used today.

How the Two Trial Types Are Different

The biggest difference between pragmatic and explanatory clinical trials is who can join. Explanatory trials are usually picky. They often exclude people who have other illnesses, who take other medications, or who fall outside a narrow age range. The reason is to keep the picture clean: if everyone in the study is similar, any change in their condition can be linked more confidently to the treatment being tested. For more on why some people qualify for trials and others do not, see Eligibility Explained: Why Not Everyone Qualifies for a Trial.

Pragmatic trials cast a wider net. They include people with the kind of mixed health profiles that doctors see in everyday practice: patients with more than one condition, people on other medications, older adults, and so on. The trade-off is that the results are noisier, but they are also more relevant to the broader group of people who will eventually use the treatment.

The two types also differ in where they happen. Explanatory trials often run at academic medical centers or specialized research clinics. Pragmatic trials tend to take place in regular doctors' offices, community clinics, or hospitals, mirroring the settings where patients normally get their care.

The rules around the treatment itself are stricter in explanatory trials. The dose, the timing, and the way the treatment is given are all standardized. Pragmatic trials allow more flexibility, letting doctors adjust the treatment the way they would normally do for a patient. Even what gets measured can be different. Explanatory trials often track lab results or short-term medical changes. Pragmatic trials are more likely to look at things patients care about directly, such as hospital visits, quality of life, or how long someone stays well.

Why Both Types Are Needed

It is tempting to think one type is better than the other, but both are needed. A treatment that does not work under careful, controlled conditions is unlikely to work in real life. So explanatory trials come first, to figure out if the treatment can work at all. But a treatment that works only in narrow, ideal conditions may not help most patients, because most patients do not live in narrow, ideal conditions. So pragmatic trials check whether the benefit holds up in the real world.

Most actual trials sit somewhere between fully explanatory and fully pragmatic. A study might be strict about who can join, which is an explanatory choice, while being flexible about how the treatment is given, which is a pragmatic choice. Researchers use a tool called PRECIS-2 to figure out where a particular trial sits on this spectrum, but the basic idea is straightforward: trials are not all-or-nothing, and design choices reflect what the researchers are trying to learn.

When Each Type Is Used

Explanatory trials are most common early in the development of a new treatment, before anyone knows whether it works at all. The first studies in humans (called Phase 1 and Phase 2) are usually explanatory, because researchers are still trying to figure out the basics: does the treatment do anything, and is it safe? Phase 3 trials, which are larger and used to seek approval from the FDA (the U.S. Food and Drug Administration), often keep some explanatory features for the same reason. Regulators want a clean answer before allowing a new treatment to be sold.

Pragmatic trials usually come later. Once a treatment has cleared the explanatory phases and been approved, the next question is how it actually performs in everyday medicine. Pragmatic trials are also commonly used to compare two existing treatments head-to-head, to test prevention or screening programs, or to evaluate new ways of delivering care. Some pragmatic studies are run after a drug has been approved, as part of ongoing safety monitoring. For more on what happens after a treatment is approved, see Phase IV Trials: Post-Approval Studies and Ongoing Safety.

One of the most well-known pragmatic trials is the Salford Lung Study, conducted in the United Kingdom. Researchers compared a new inhaler against the inhalers patients were already using for asthma and COPD (a chronic lung disease that makes it harder to breathe). The study took place in everyday family doctors' offices, with patients who reflected the real-world population, and used the patients' electronic medical records to track results. The study traded some precision for relevance: the answers were noisier than a tightly controlled trial, but they spoke directly to how the inhaler would perform once it was prescribed in normal medical practice.

Why This Matters If You Are Looking at a Clinical Trial

For someone thinking about joining a clinical trial, knowing whether the trial is explanatory or pragmatic helps make sense of what the study will actually involve. An explanatory trial is more likely to require frequent visits, strict rules about other medications, careful tracking, and detailed measurements. A pragmatic trial is more likely to feel closer to normal medical care, with visits roughly on the same schedule as regular appointments. For more on what to compare when weighing trial participation against your usual care, see Clinical Trial vs Standard Care: What Patients Should Know.

It also helps explain why two studies of the same treatment can show different results. Both can be true at the same time, because they were measuring different things. A treatment with a strong explanatory result and a weaker pragmatic result is one that can work when everything goes right but loses some of its punch when used in everyday life. That is useful information, not contradictory information.

For doctors and patients making treatment decisions together, the type of trial behind a recommendation matters. A pragmatic trial result is closer to what a typical patient might experience. An explanatory trial result tells you what the treatment is capable of when conditions are ideal. Both are worth knowing, and most decisions benefit from looking at both kinds of evidence.

How to Find Clinical Trials

If you want to look at clinical trials that may be a fit for your situation, there are a few places to start. Talking to your doctor is one. Doctors who follow research in their field often know about trials that are recruiting locally and can tell you whether one might be relevant to you. For a step-by-step walk-through of how the search and enrollment process works, see How to Find and Enroll in a Clinical Trial: A Step-by-Step Guide.

DecenTrialz is another option. It is a website that helps connect people with clinical trials they may be eligible for. You share some basic information about your health and where you live, and the system shows you trials that could fit. Before anything is handed off to a research team, a nurse walks you through what each study involves, so you can decide whether to take the next step. The research team running the trial makes the final decision about whether you can join. You can start a search at decentrialz.com.

Next Steps

Pragmatic and explanatory clinical trials are two ways of answering different questions about a treatment. Explanatory trials test what a treatment can do when conditions are ideal. Pragmatic trials test what it does in real life. Both kinds of evidence matter, and knowing the difference helps make sense of news about new medications and clinical research.

If you are thinking about joining a clinical trial, or want to see what studies might be a fit for a specific condition, you can begin a search at decentrialz.com.