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Clinical Studies and Clinical Trials

There is a lot we still don’t know about people and their health. Different forms of medical research help us learn more.

Preclinical Studies

Before a treatment can be prescribed by doctors, and before it can even be studied in humans, scientists must make sure it will not cause serious harm. To do this, they test the treatment in cells (in vitro) and in animals (in vivo). Preclinical studies must provide detailed information on dosing and toxicity (if the treatment is harmful). Researchers look at these results to decide if the treatment is safe to be tested in people.

Clinical Studies

Scientists spend a lot great deal of time studying models of disease in animals and cells, and it is important to do so. But it is also necessary to study how an intervention (a drug, device, therapy, etc.) works in actual people. Studies that involve people—human subjects—are called clinical studies. There are two main types of clinical studies: observational studies and clinical trials.

Observational Studies

Sometimes a scientist wants to understand more about how different aspects of people’s lives affect their disease. This could be medications they’re taking, their age and gender, or lifestyle choices such as diet and exercise. In an observational study, scientists may ask patients to answer questions and have tests over time. Then the scientists think about how the different factors affect the patients’ disease. 

For example, researchers could observe a group of people who have had Parkinson’s for 20 years or more to try to understand the factors (age of disease onset, medications used, living situation, symptoms, etc.) that impact their long-term survival. Any insights gained can ultimately be used to improve health care delivery for this group. In fact, this study is being done right now as part of the largest observational study every conducted in Parkinson’s disease: NPF’s Parkinson’s Outcomes Project.

Clinical Trials

Sometimes as a result of information learned in an observational study, or from studying animals or cells in a preclinical trial, a scientist will figure outdevelop a promising new treatment for a disease. This could be a drug, surgery or therapy like exercise or diet guidelines. To make sure it works, the scientist will conduct a clinical trial, also known as treatment research or an interventional trial. When a clinical trial is used to study medications and medical devices, the study is conducted in phases. The trials at each phase help scientists answer different questions about the drug or device. To learn about the phases of clinical trials, visit our page on drug development.

Why are clinical studies important?

All types of research are critical for improving care. Basic science research—tests done in a laboratory—can help us learn more about the human body and the causes of Parkinson’s disease. Basic science research can also point scientists in promising directions as they develop and refine treatments.

Clinical studies are essential because through them, discoveries made in the laboratory can help people with Parkinson’s today and in the future. NPF is at the forefront of Parkinson’s research, and clinical studies are central to our vision. NPF’s Parkinson’s Outcomes Project was the first study of its kind and continues to be the largest. Every year, insights from the Project help optimize Parkinson’s care, leading to better quality of life for people with Parkinson’s today and better health for people with Parkinson’s tomorrow. 

Why should I participate in a clinical study?

We can only reach breakthroughs in treatment and care if people are willing to participate in the studies!

Participating is safe and can help you

Every clinical study is reviewed thoroughly before your doctor is allowed to ask you to participate. Clinical trials may have some risks, but your doctor is required by law to explain the risks to you clearly and make sure that you understand them. If your doctor tells you about the risks of participating in the study, ask yourself, “What are the risks of NOT participating in the study?” Most of the time, if you balance the possible benefits from participating against the risks, it is about the same as the risks of not being in the study. On the other hand, the study may be of a new drug or treatment that could help you, and if you don’t participate, it may be years before you have a chance to get that drug.

Some people do not participate because there is no guarantee that you will get the experimental therapy; you might get the placebo. Again, think carefully about the risks and benefits of entering the study and getting the new treatment, entering the study and getting the placebo or not entering the study at all. 

By participating, you are helping others

If you have Parkinson’s or any other disease, the drugs, procedures and therapies you use now were tested scientifically, likely by thousands of volunteers. Participating in a clinical trial is your way to pay it forward for people diagnosed with Parkinson’s in the future. 

What should I think about before participating in a clinical study?

Talk to your doctor first. Sometimes you may find out about research from the internet or an advertisement. You should talk to a doctor you trust before you agree to participate.

Look for research that is done at a reputable institution. NPF Centers of Excellence and other top academic medical centers are trustworthy institutions that have rules in place related to protection of human research subjects. If you are recruited for a clinical trial by your local doctor, look up the trial on If the doctor leading the trial is not affiliated with a reputable university or major research hospital and the trial is not listed in, you should be careful.

Read the consent form carefully. It is important that no one forces you to participate. Before you sign up, you will be part of the “informed consent” process. The consent form should be written in language you understand. The researchers should explain the risks and benefits of the study. Ask questions if something is confusing or unclear, and take time to understand what you are signing up for. Understand your rights if you agree to participate now but wish to withdraw later.

Where can I find a clinical study to sign up for?

NPF’s Parkinson’s Outcomes Project is the largest clinical study ever conducted in Parkinson’s disease. The goal of the study is to identify and explain factors that result in longer, better and more active lives for people with Parkinson’s. Twenty NPF Centers of Excellence are participating in the study. is a registry and database of publicly and privately support clinical studies conducted around the world. This website is a service of the National Institutes of Health (NIH) and is the best place to find up-to-date information on trials that you might participate in. NIH Clinical Trials and You provides a step-by-step guide to finding a trials on

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