Clinical Trials

Clinical Trials

There is a lot we still don’t know about health and Parkinson’s disease (PD). Different forms of medical research help us learn more. Types of medical research include:

Preclinical Studies

Before doctors can prescribe a treatment 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 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 great deal of time studying models of diseases in animals and cells. It is necessary to study how an intervention (a drug, device, therapy) works in 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. Areas of interest can include a person’s medications, age and gender or lifestyle choices, such as diet and exercise. In an observational study, scientists may ask participants to answer questions and have tests over time. Then the scientists study how different factors affect the participants’ disease. 

For example, researchers could observe a group of people who have had PD for 20 years or more 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. A study like this is being done right now as part of the largest observational study ever conducted in PD, the Parkinson’s Foundation Parkinson’s Outcomes Project.

Clinical Trials

Sometimes as a result of an observational study or from studying animals or cells in a preclinical trial, a scientist will develop 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, it is conducted in phases. The trials at each phase help scientists answer different questions about the drug or device.

How are clinical trials conducted?

Clinical trials that test drugs are conducted in a series of carefully monitored phases designed to answer specific questions.

Phase I trial: researchers test a new drug or treatment in people for the first time. A small group of people, typically fewer than 100, are monitored to evaluate the drug or treatment's safety, determine a safe dosage range and identify side effects.

Phase II trial: study the effectiveness of a drug or treatment in a larger group of people.

Phase III trial: the study drug or treatment is given to a large group of several hundred to several thousand people. This large-scale testing gives more detailed information about the drug's benefits, effectiveness and range of possible side effects.

Phase IV trial: usually conducted on drugs that have already been FDA-approved. These trials are run to determine additional uses for an approved drug or further study its safety in large numbers of participants.

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 PD. Basic 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 PD today and in the future. The Parkinson’s Foundation is at the forefront of PD research and clinical studies are central to our vision. The foundation’s Parkinson’s Outcomes Project was the first study of its kind and continues to be the largest. Every year, insights from the study help optimize PD care, leading to better quality of life for people with PD today and better health for people with PD tomorrow. 

Benefits and Risks of Clinical Trials

Participating in a clinical trial can be a rewarding experience. Consider the following benefits when deciding if you should join a clinical trial:

  • You will have access to leading healthcare professionals, cutting-edge new treatments and high standards of care.
  • Joining a clinical trial can increase your knowledge and understanding of your disease.
  • People who take part in clinical trials are contributing to science that may benefit themselves and others. The medications that you take now are available only because people before you have volunteered in clinical trials.

Although every effort is made to ensure that clinical trials are as safe as possible, clinical trials that test new therapies are experiments and can involve risks.

Here are some of the risks to consider:

  • There may be undesirable side effects to the treatment. A health professional will explain possible risks and side effects during the informed consent process.
  • The treatment may not be effective for the participant.

People with PD should also keep in mind that they may not receive the experimental treatment because they may be randomly assigned to the control group and receive either a different dose of the test treatment (a treatment that is already available and considered standard therapy for the disease, or a sugar pill (placebo)). The control group is used as a basis for comparison. In many studies, the researcher is not aware of who is taking the treatment and who is in the control group. The study might have time and travel requirements that are demanding. These are issues you should address when talking to a clinical investigator.

Why should I participate in a clinical study?

We can only reach breakthroughs in treatment and care if people participate in the studies.

Participating is safe and can help you.

Every clinical study is reviewed thoroughly before your doctor asks you to participate. Clinical trials carry 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. If you don’t participate, it may be years before you have a chance to try that drug.

Some people do not participate because there is no guarantee they will get the experimental therapy; they 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. 

Your participation can help others

If you have PD or any other disease, the drugs, procedures and therapies you use now were scientifically tested, 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. Talk to a doctor you trust before you agree to participate.

Look for research studied conducted by a reputable institution. The Parkinson’s Foundation’s Centers of Excellence and other top academic medical centers are trustworthy institutions that have rules in place related to the 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, be careful and do your research.

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 a language you understand. The researchers should explain the risks and benefits of the study. Ask questions if something is confusing or unclear. Take time to understand what you are signing up for. Understand your rights if you agree to participate now, but wish to withdraw later.

How can I learn more about clinical trials?

If you are interested in research, you may want to consider applying to become a Research Advocate, so you can be trained to influence research and speed new and effective treatments for PD.

Browse information about the Parkinson's Advocates in Research program to learn how you can get involved.

Where can I sign up for a clinical study?

The 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 PD. Twenty 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 enrolling participants. NIH Clinical Trials and You provides a step-by-step guide to finding trials on

Fox Trial Finder
Web-based clinical trial matching tool to connect those with and without PD to Parkinson’s clinical research opportunities that urgently need participants. After volunteers input information about themselves (zip code, date of birth and brief medical history), Fox Trial Finder provides trial match suggestions. Volunteers can connect directly with trial coordinators through a secure messaging interface. Register today to play a part in accelerating recruitment into PD clinical research.

An information service for patients, pharmaceutical companies and research centers involved in clinical research. Centerwatch publishes a wide range of newsletters, books and directories.

  • Review an extensive list of clinical trials being conducted across the world.
  • Subscribe to a free email service which notifies you about new PD clinical trials in your area.

National Institutes of Health
A resource site developed by the National Institutes of Health to provide patients, family members and the public with current information about clinical research studies.

  • Find out about current PD clinical trials.
  • Access information describing the clinical trials process.

Parkinson Study Group (PSG)
A nonprofit, cooperative group of PD experts from medical centers in the U.S. and Canada dedicated to improving PD treatments through clinical trials.

  • Identify references in scientific and academic journals relating to PD research and clinical trials.
  • Find out about ongoing PSG clinical trials.

Page reviewed by Dr. Chauncey Spears, Movement Disorders Fellow at the University of Florida, a Parkinson’s Foundation Center of Excellence.

For more insights on this topic, listen to our podcast episodes “Repurposing Medications to Slow Progression of PD,” “The Golden Year for Testing Disease Modifying Drugs,” “Understanding Biomarkers to Deliver Precise Treatments,”  “What is a Disease Modifying Therapy in PD?,” "The Skinny on Clinical Trials on PD" and “Retention Rates in Longer Clinical Studies.”


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