Clinical research, explained

How clinical research works.

Most people have never had this explained to them. So we start at the beginning, and we use plain words the whole way down.

Start here

What a clinical trial is.

A clinical trial is a research study. It tests whether a new treatment is safe and whether it works.

That is the whole idea. Everything else on this page is detail.

Doctors cannot know if a new treatment helps people until people try it. A trial is the careful, supervised way of finding out. It is run to a written plan, it is watched by people who do not work for the drug company, and every person in it chose to be there.

A trial answers three questions.

Every study, for every condition, is built to answer the same three things.

The three questions every clinical trial asksThree panels reading: Does it work? Is it safe? What are the side effects?1Does it work?Better than what we havenow, or not?2Is it safe?Safe enough to be worththe benefit it gives.3Side effects?Which ones, how often,and how serious.
Figure 1. Does it work, is it safe, and what are the side effects. Every trial is built around these three questions.

Every medicine in your cabinet is there because people volunteered for a study that proved it worked.

Why this exists

This is not a new idea.

People often picture clinical research as something modern and experimental. It is neither.

The first one ran in 1747. A ship’s doctor named James Lind wanted to know why sailors were dying of scurvy. He split twelve sick sailors into pairs and gave each pair something different. The pair who got oranges and lemons got better.1

That was the whole study. Take a group, give them different things, watch carefully, and see who improves. Trials today are far larger and far more carefully watched, but the shape of the thing has not changed in almost three hundred years.

International Clinical Trials Day is May 20th, the day Lind started.1

It takes a long time to get here.

A treatment does not go from an idea to your pharmacy quickly. From the first study in people to the day a doctor can prescribe it takes between five and twenty years.2 The FDA approves around forty-five to fifty new treatments a year.3 In a typical year there are up to six thousand studies running in the United States.4

By the time a study reaches a clinic near you, years of work have already gone into it, and a lot of people have already checked it.

The four phases

Studies go in order, and they get bigger.

A treatment has to finish one phase before it is allowed to start the next. Nothing skips ahead.

The four phases of a clinical trial by size and lengthPhase 1, 20 to 100 participants, up to 1 year. Phase 2, 100 to 300 participants, 1 to 2 years. Phase 3, 300 to 3,000 participants, 1 to 4 years. Phase 4, 3,000 or more participants, after approval.Phase 120 – 100 peopleUp to 1 year · Is it safe, and at what dose?Phase 2100 – 300 people1 – 2 years · Does it actually work?Phase 3300 – 3,000 people1 – 4 years · The final proofThe FDA reviews everything above this line before approving anything.Phase 43,000+ people, after approvalLong-term safety, once the treatment is in normal use.Bar length shows roughly how many people take part.
Figure 2. Phase 1 runs with 20 to 100 people for up to a year. Phase 2, 100 to 300 people over one to two years. Phase 3, 300 to 3,000 people over one to four years. Phase 4 runs after approval, in 3,000 or more people.5 Sometimes phases 2 and 3 are combined into one study.5

Where you would come in.

Almost every study advertised to the public is phase 2 or phase 3. That means the treatment has already been through safety testing, the FDA has already allowed it to be given to people, and hundreds of others have taken it before you.

People picture themselves at the very start of the line. Almost always, they would be joining near the end of it.

Step by step

What taking part actually looks like.

Every study runs through the same five stages, in the same order.

The five stages of taking part in a clinical trialScreening, informed consent, randomization, treatment, then follow-up.1ScreeningThey check whether you are a fit. Age, health, history, current medicines.2Informed consentThey explain the risks, the benefits and the schedule. Then you decide.3RandomizationA computer assigns you to a group, purely by chance.4TreatmentYou take part on a set schedule. The team checks on you throughout.5Follow-upA last check, and you are handed back to your own doctor.
Figure 3. The five stages of a study, in order.6 You can stop at any stage, including after you have signed.

Screening comes first, and most people stop here.

Every study has a written list of who can join and who cannot. It is called the eligibility criteria. It covers things like your age, your condition, how long you have had it, and what else you take.6

Not qualifying is normal. It is not a judgement about your health. It usually means the study needed someone slightly different, and it costs you nothing to find out.

Then you decide, in writing.

Before you agree to anything, the team has to give you a document that explains the whole study. What it is testing. What could go wrong. What you would have to do, and for how long.

You are allowed to take it home. You are allowed to read it with your family or your own doctor. Nobody should rush you, and you can say no after signing it.

What is in the consent form

What the study is testing. The treatment, the condition, and the phase.

What the risks are. Every known side effect, from the common ones to the rare ones. Read this part slowly.

What you would do. The visits, the tests, the schedule and the total length.

What it pays and what is covered. Ask for the amount per visit and the total, and ask whether study care costs you anything.

Your rights. That you can leave at any time, for any reason, without it affecting your normal care.

Who approved it. The form names the ethics board that reviewed the study, and gives you their phone number. If there is no name and no number, walk away.

Randomization

Why a computer picks your group.

Randomization means you are put into a group purely by chance. No person chooses for you.

Think of it like drawing names out of a hat to make two teams. If you do not mix the names first, one team might end up with all the strong players, and the game tells you nothing.7

A study works the same way. If a doctor got to choose who received the new treatment, they might put the healthier people in one group without meaning to. Then nobody could tell whether the treatment worked or whether that group was simply healthier to begin with.

How randomization splits participants into balanced groupsA mixed pool of participants is divided by a computer into two groups with a similar mix of people in each.Everyone who joinedComputerGroup A — the new treatmentGroup B — the comparison
Figure 4. The computer splits everyone by chance, so each group ends up with a similar mix of people.7 That is what makes the result mean something.

Randomization is not the study being careless with you. It is the one thing that makes the answer trustworthy.

Placebos and blinding

The sugar pill question.

A placebo looks and feels exactly like the real treatment, but there is nothing active in it.8

This is the part that worries people most, so here is the plain version.

A placebo is there so researchers can tell the difference between the treatment working and people simply feeling better anyway. If everyone got the real thing, there would be nothing to compare it against.8

Many studies do not use one at all. When a study does, it is written in the consent form and the team has to tell you before you agree to anything.9

Blinding, and why nobody tells you which group you are in.

In most studies you are not told which group you were put in. That is called being blinded. When your study doctor is not told either, it is called a double-blind study.9

It sounds like something is being kept from you. What it actually does is stop expectation from bending the result. If you knew you had the real treatment you might report feeling better. If your doctor knew, they might record your symptoms a little differently without ever meaning to.

Open, single-blind and double-blind studiesIn an open study both you and the doctor know the group. In a single-blind study only the doctor knows. In a double-blind study neither knows until the study ends.Who knows which group you are inYouYour study doctorOpenKnowsKnowsWhen hiding it is not possibleSingle-blindDoes not knowKnowsDouble-blindDoes not knowDoes not knowThe most common design
Figure 5. Three designs. In a double-blind study neither you nor your doctor knows, until the study is over.9 Safety always overrides this: if the team needs to know in an emergency, they can find out immediately.

You are told before you agree

Whether the study uses a placebo is explained during informed consent. Nobody is slipped into one.9

Everyone gets the same care

The visits, the tests and the attention are the same in both groups. Usually the only difference is the treatment itself.6

You keep your own medicine

In most studies you stay on what you already take, and the study treatment is added on top.

You can simply say no

If you do not want to be in a placebo study, do not join one. Ask the question first.

Who is watching

Nobody runs a study on their own.

There are four separate groups involved, and they do not work for each other. That is the entire point of the arrangement.

The four groups involved in overseeing a clinical trialThe drug company pays for the study but does not run it. The clinic runs it and sees you. The ethics board approves and monitors it. The FDA can inspect or stop it.The drug companyMakes the treatment and pays forthe study. Does not run it. Nevermeets you.The clinicThe doctor and coordinators youactually see. They run the studyand answer to the two below.The ethics boardDoctors, ethics experts andordinary people, separate fromthe study. Approves it first.The FDAAllowed it to start. Can inspectthe clinic or stop the study atany time.
Figure 6. Four separate groups, none of which reports to another. The ethics board reviews the study before a single person joins, and keeps watching after it starts.8

The rules are older than any company involved.

Ethics boards work from the Declaration of Helsinki, written by the World Medical Association to protect people in medical research.10 No study is allowed to start until a board that has nothing to do with it has read the plan and agreed.

You can look any study up yourself.

Every real study in the United States is registered publicly on ClinicalTrials.gov, with its plan, its locations and who is paying for it. If someone offers you a study you cannot find there, that is worth asking about.

Your study doctor has one job, and it is not the data. It is you. If taking part stops being good for you, the study stops for you.

Who takes part

Studies are not a last resort.

A lot of people believe trials are only for those who have run out of options. That is not what most studies are.

Most are for ordinary, common conditions. High blood pressure. Diabetes. Eczema. Migraines. Trouble sleeping. Many people who join are already doing fine on their current treatment, and the study is testing whether something new does better.

Some studies need healthy volunteers instead, to check that a new treatment is safe before anyone with the condition takes it.6

It matters who takes part.

Treatments do not work the same way in everybody. Age, genetics and other health conditions all change how a medicine behaves in the body. If a study only enrolls one kind of person, nobody can be sure the results apply to anyone else.

Not everything happens at a clinic any more.

Study visits used to mean driving somewhere every time. Since 2020 far more studies allow some visits by phone or video call, which has made taking part possible for people who cannot travel easily.11

Tether is a nonprofit directory. We do not run studies and no clinic pays us to send you. We tell you what is out there and hand you the clinic’s own phone number.

Before you say yes

Six questions worth asking.

A good study team answers all of these without hesitating. If a question seems to annoy them, that itself is an answer.

What phase is this study?

Phase 2 or 3 means a great deal is already known about the treatment.

How long is the whole thing?

Not just the treatment part. Include the follow-up.

How many visits, and how long is each?

Ask for the total number of in-person visits. That is the real commitment.

Is there a placebo group?

If there is, ask what your chances are of getting the real treatment.

What does it pay, and what does it cost me?

Ask the amount per visit, the total across the study, and whether study care is free.

Can I leave whenever I want?

The answer is always yes. Any other answer means you should walk away.

Where these numbers come from

  1. Bhatt A. Evolution of clinical research: a history before and beyond James Lind. Perspectives in Clinical Research, 2010;1(1):6–10.
  2. Brown DG, et al. Clinical development times for innovative drugs. Nature Reviews Drug Discovery, 2022;21(11):793–4.
  3. U.S. Food and Drug Administration. Novel Drug Approvals at FDA, February 2025.
  4. World Health Organization. Number of clinical trials by year, country, WHO region and income group, June 2024.
  5. U.S. Food and Drug Administration. Step 3: Clinical Research, January 2018.
  6. National Institutes of Health. NIH Clinical Research Trials and You, May 2025.
  7. National Cancer Institute. How Do Clinical Trials Work?, November 2024.
  8. Gupta U, Verma M. Placebo in clinical trials. Perspectives in Clinical Research, 2013;4(1):49–52.
  9. National Institutes of Health. NIH Clinical Research Trials and You, May 2025.
  10. World Medical Association. Declaration of Helsinki: Medical Research Involving Human Participants, May 2025.
  11. Thomas D, McDonald VM, Gibson PG. Telehealth and remote visits in clinical research, 2024.

That is how it works.

Answer a few questions and we will tell you which studies near you you might fit, and which you would not.

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