What are clinical trials?

Clinical trials study potential new treatments in health volunteers and/or people with a specific illness or condition. These treatments already have had some positive effects on a disease in lab or animal experiments. Clinical trials are the next step in the drug development process to see if a treatment generally safe and effective in people.

Different phases in clinical development

It takes a lot of research to develop a new treatment. Clinical trials are done in several steps, also called “phases”. Each phase has a specific purpose, such as to look at how well the treatment or drug works, what is the best dose and what side effects may occur.


Before clinical trials can be done with human participants, researchers study new treatments in the lab. This is called “pre-clinical development”. Once the researchers have enough information, they ask for permission to do clinical trials from the health authority and independent groups called ethics committees.


Phase 1 trials are usually the first time a new treatment is studied in humans. These studies are typically conducted on small populations of healthy humans to learn what the body does to a drug, such as how it is absorbed, processed and how it passes out of the body.


After the successful completion of Phase 1 trials, Phase 2 trials are done in a slightly larger population to learn if a new treatment helps people who have the disease or condition for which the treatment was developed. These trials are also designed to keep learning about side effects people have while using a treatment.


Phase 3 trials are done to confirm that a new treatment helps people who have the disease or condition for which the treatment was developed. They are designed to learn how a treatment works compared to the standard therapy currently being used for the disease or compared to a “placebo”. A “placebo” is designed to resemble the treatment but does not have any real effect. These trials are also designed to keep learning about side effects people have while using a treatment. The results of these trials usually provide the information that is included in the package insert and labelling.


Phase 4 trials are done after a treatment has been approved for all people to use. These trials take place over many years. They are done to learn how a treatment works when people are taking it as part of their everyday lives.
Sometimes these trials are “observational” studies. The people in observational studies are prescribed the treatment in the usual manner. They are not assigned to a treatment by the researchers.

Frequently asked questions

Clinical trials play a key role when developing a new drug. Yet, despite being necessary, tests involving humans are often viewed critically. How do we ensure the highest ethical standards for clinical trials?
During a clinical trial, the participants get treatments and tests according to a “protocol”. A protocol describes what will be done in the trial and how. Everything is planned very carefully to keep participants as safe as possible. Some trials compare a new treatment to a standard one that is already available. Other trials compare a treatment to a “placebo”. A placebo is designed to resemble the treatment but does not have any real effect. Some trials just look at a treatment without any comparisons.
It can take months or even years to do a clinical trial. And, a trial can go on for much longer than each participant is in it.
The length of a trial and the amount of time the participants are in it depends on how long it takes for researchers to collect all the information they need.

The length also depends on:
  • Which step in the research process the trial is in. The steps are called “phases”. Phase 1 and 2 trials are shorter than Phase 3 and 4 trials.
  • The type of disease and treatment in the trial. Some treatments need to be studied over a long time to find out if they were safe and helped participants with certain disease. But other diseases and treatments can be studied in a short time.
  • The number of participants needed in the trial. Some trials need to collect information from thousands of participants. These trials take longer to make sure the researchers get information from enough participants.

Once a trial is finished and all the participants have completed their part, the researchers review all the information that was collected. This can also take many months. If the sponsor seeks approval for the drug so it can be used in all patients, it can take months for the drug to be reviewed and approved by the governments health agency.
Clinical trials take place in doctors’ offices, medical centers, community hospitals and clinics. They may be done in one place or in hundreds of places at the same time. Each location has a research team. The research team includes doctors, nurses, and other health care professionals. The research team collects information from the participants during the trial to study if the treatments are working and are safe.
Clinical trials can be sponsored by physicians, medical institutions, foundations, non-profit organizations, pharmaceutical companies, and government agencies. A sponsor oversees or pays for a clinical trial and collects and analyzes the data.
Requirements, also called “eligibility criteria”, can be about age, gender, the type and stage of a disease, previous treatment, and other medical conditions.

“Inclusion criteria” are the requirements a person must have to be in a trial. By allowing only certain participants in a trial, researchers can be sure the effects of the treatment are not influenced by other factors.

“Exclusion criteria” are requirements that might prevent a person from being in a trial. These criteria protect people who may be made worse if they were in a trial.
Medically speaking, children are not just “little adults”: the composition of their bodies and maturity of their organs not only differ from those of adults quantitatively, a number of diseases only occur in children or progress differently in children than in adults. Children also need special protection because of their intellectual and emotional limitation to provide informed consent. Therefore, especially strict regulations and ethical standards have been developed for pediatric studies.
Is animal testing really necessary? And how has it developed over the last years? This short video will anwers your questions.
“Informed consent” is a process to make sure you understand important information about a clinical trial and agree to be in the trial. Information may include the purpose of the trial, the treatments used, and the potential risks and benefits. After you have a conversation with the clinical trial staff, all clinical trial participants must sign an informed consent form. Signing the form does not mean a participant must stay in the trial. Participants can leave a clinical trial at any time. The research staff will discuss with them what continued care they may need for their condition/disease and will continue to monitor them after they leave the study in case they have any delayed side effects. If new benefits, risks, or side effects are discovered during the trial, the researchers must tell the participants. Participants may need to sign a new informed consent form to stay in the trial.
We do clinical trials all around the world, as they need to be representative for the people intended to use a new medicine.
Medical research done in people must follow strict rules. Every clinical trial has a plan called a “protocol”. The protocol is a set of instructions that everyone in the trial must follow. It is the plan for how the trial will be carried out.

The protocol describes what will be done in the trial and how. It also describes why each part of the trial is necessary.

Before it begins, a trial must be approved by a health authority and other organizations. Different countries require different approvals. Approvals ensure that trial participants will be treated well and that the study treatment is worth the risk.
Yes. Every clinical trial must be approved and overseen by an “Institutional Review Board”, also called an “IRB”. An IRB is an independent group that makes sure a clinical trial is safe enough to be worth any risk to participants. These group can also be called an “Independent Ethics Committee”, or an “IEC”. The group can include doctors, statisticians, community advocates, and others. They review and approve the trial plan, called a protocol, and the materials that might be given to the participants. They also make sure that the participants are treated well while they are in the trial.
Yes. A participant can leave a clinical trial at any time without giving a reason. The participant should tell the research team if they want to leave and it would be helpful if the participant told the team why he/she is leaving.
Yes. Participants should still see their primary care doctor. Most clinical trials only give treatment for one condition over a short time. They do not give other medical care like primary care doctors. Primary care doctors can work with the research team to make sure that a participant’s other medications and treatments will not conflict with the clinical trial protocol.
No. “Standard of care” is a treatment that has already been tested and approved by the health authority. Treatment in a clinical trial is still being tested.

When you go to your regular doctor, you get a standard of care. For example, you may get a cast if you break your arm. We know how a cast works for most people.

When you participate in a clinical trial, you get care that is still being studied. For example, you may get a new drug to see if it stops breast cancer from coming back. We don’t know how the new drug works.
Yes. Every clinical trial has a carefully designed plan called a “protocol”. The protocol describes what will be done in the trial and how. It may include the:
  • Types of people that can participate in the trial
  • Schedule of tests, procedures, medications, and dosages
  • Length of the trial
The protocol is designed to protect the trial participants and answer specific research questions. Everyone in the trial follows the same protocol.
A “placebo” is designed to resemble the treatment but does not have any real effect. In clinical trials, new treatments are often compared with placebos. Some participants are given a placebo instead of a treatment. This helps make sure that any effects are actually caused by the treatment being studied.
A “control” helps researchers compare a study treatment. In many clinical trials, one group of participants gets a study treatment and a “control group” of participants gets a standard treatment or a placebo. Researchers compare the results of both groups to see if a study treatment works better.
“Expanded access protocol” allows people to take a study drug even if they can’t participate in the clinical trial. These people may not be able to participate in the trial because of their age, other health problems, or other reasons. But the study drug may still help them. Makers of new drugs can give “expanded access” to patients if researchers are studying or have finished studying the drug in a clinical trial. There must be evidence that the drug can help these patients and is worth any risk.
Clinical trials involve a lot of people who do different things. Each person plays an important role. The principal investigator, also called a PI, is responsible for organizing and leading the trial as well as recording and studying the data. The PI also directs the team. Like a team manager, the PI follows a playbook, which is called the study “protocol”. The protocol is a set of instructions that everyone in the game must follow. It’s the plan for how the study will be carried out. The research staff members are like assistant managers who help the PI. The clinical research coordinator handles the day-to-day activity at the research site. He or she has easy access to the PI and is the main contact for participants. If you have questions about the trial or your health, ask the clinical research coordinator.
Some trials pay for the participants’ travel costs, time and commitment. Not all do. The amount paid varies.
Participants should:
  • Plan ahead and write down questions to ask.
  • Ask a friend or relative to come along for support and to hear the responses to the questions.
  • Bring an audio recorder to record the discussion to replay later.
  • Participating in a clinical trial takes time and commitment.
  • The clinical trial could end at any time. Even if you want to continue to participate, the company making the drug could stop the trial.
  • Clinical trial participants may not feel better.
  • All trial participants should let their doctors know that they are participating in a trial.
  • Participants may get access to a new drug that is not available to other people because it is not on the market yet.
  • Study doctors and nurses will closely monitor your health during the clinical trial.
  • Results of the clinical trial may help other people for their health problems in the future as it adds to medical knowledge about diseases.
  • The new treatment may not work for you.
  • As any drug, a new treatment may have expected and unexpected side effects..
  • In some trials, participants don’t know whether they receive the new treatment or are assigned to get placebo or standard therapy currently used instead.
  • Depending on countries and health insurance systems, participants may need to cover some of the costs.
  • Participants may need to visit the doctor more often than if they were not in a clinical trial.
Do you know that we publish summary reports of our trials online to support transparency and foster scientific discoveries? We do this regardless of positive or negative outcomes.

Participate in a Bayer trial

Bayer clinical trials study a new treatment’s safety or how well it helps people with a disease/condition. The treatment may be a drug, medical device, or new way of using an existing treatment. You can volunteer to participate in a clinical trial.

Find a Bayer trial that might be right for you.