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Parkinson's clinical trials

Clinical trials

There is currently no cure for Parkinson’s so research into new and improved treatments is vital. There are many Parkinson's clinical trials (also known as clinical studies) currently underway throughout the world. These aim to improve the accuracy of diagnosis, develop new treatments and ultimately bring us close to a cure for the condition.

Clinical trials are required in order to find out whether a new treatment:

  • is safe
  • is beneficial to people with Parkinson’s
  • is more effective than the current treatments for some people
  • improves the quality of life for people with Parkinson’s.

Clinical trials are designed according to a strict protocol or process, ensuring that new treatments are tested in a controlled way to minimise any risk to participants. The effect of the treatment is carefully monitored and, in addition to determining their effectiveness, data is collected on safety aspects such as adverse reactions and interaction with other medications. Sometimes a trial will study the effects of using an existing treatment in different ways such as a new formulation of the drug.

Clinical research is an expensive process which requires considerable financial investment. This comes from a range of sponsors including the pharmaceutical industry, governments, academia and research organisations.

How might clinical trials help in Parkinson’s?

Clinical trials can help people with Parkinson’s in many ways. Some of the benefits include:

  • broadening our understanding of Parkinson’s so that existing treatments can become more effective
  • giving people with Parkinson’s the opportunity to be involved in research which uses the most up-to-date treatments and devices
  • helping to improve the quality of life for people with Parkinson’s
  • improving treatment for future generations of people with Parkinson’s
  • leading us closer to a cure.

The trial process

All medications must undergo rigorous testing before they can be approved for use. The trial process is lengthy, complex and carries significant costs to the pharmaceutical industry. Only a small minority of treatments reach the final stages of a trial and ultimately receive approval to be marketed for routine clinical use.

There are three primary stages of drug development.

1. Developing and testing a compound in a laboratory

The initial research stage, which is usually carried out in the laboratory, tries to identify which chemical compounds may be the most promising for the development of new therapies. This may be due to their chemical structure, their mechanism of action or previous studies on the chemical which may suggest that it may be beneficial for the treatment of the nerve cells which die in Parkinson’s. This is likely to include a detailed analysis of research papers which have been published for that compound.

However, there is some evidence that drugs which have been developed for other conditions may also be beneficial for the treatment of Parkinson’s – this is termed “drug repurposing”. This is usually based on our growing understanding of how drugs work and also the changes that occur during the early stages of nerve cell death in Parkinson’s. These drugs are more likely to modify the rate of progression of the disease rather than treat the symptoms.

A third group are classed as Advanced Therapy Medicinal Products (ATMPs). These include products that will replace the cells that have died or alter the genetic make-up of the nerve cells to protect them. These agents are currently at an early stage of development.

2. Pre-clinical animal testing

Initial pre-clinical studies are usually carried out in nerve cells grown in the laboratory. These provide evidence of whether a drug may rescue nerve cells which have been treated with toxins. Once a small number of promising compounds have been identified, subsequent studies are carried out in animals - often mice, rats and occasionally monkeys - to see if the treatment works as predicted. Guidelines are in place to ensure that the 'Three Rs' principles are adhered to – to reduce, refine or replace the number of animals that are used in pre-clinical drug testing. Such tests will also monitor any adverse effects to other organs and may provide indicators of potential side effects which can be monitored in subsequent clinical trials. In the past, animal models were based on the use of toxins to kill dopaminergic nerve cells in the midbrain in order to mimic the later stages of Parkinson’s. This would provide evidence as to whether a drug can help to overcome some of the movement problems associated with Parkinson’s, that is to treat the symptoms of the condition. However, more recent models involve the genetic modification of animals to allow the assessment of whether a new drug may actually act at an earlier stage of the disease in order to influence the rate at which it progresses, that is whether they are "disease-modifying” drugs.

If pre-clinical tests appear to be safe and therapeutically effective then the pharmaceutical company must apply to the appropriate national or international body for permission to begin human trials. The licensing procedure for drugs to treat Parkinson’s in Europe is governed centrally by the European Medicines Agency (EMA), although clinical trials are registered and approved at a national level. In the USA, the regulatory authority is the Food and Drugs administration (FDA). The study plan or protocol provides information regarding the pre-clinical studies that have been carried out to date, why it is believed that the treatment being assessed might be effective for a particular condition, the anticipated risks and benefits for participants ink the clinical trial, the eligibility criteria for participating in the study, the process by which volunteers are recruited for the trial, and how long the trial should last. It is important that there is significant patient input into the trial design, particularly to determine how the effectiveness of the drug will be measured. Patient involvement in all aspects of trial design is mandatory in most European countries.

3. Clinical trials (testing in humans)

Once it has been established that the compound is safe in animals and likely to have clinical benefit, permission can be sought to carry out human trials. Clinical trials are usually broken down into four different phases.

  • Phase I - the aim of this phase is to assess the safe dose of the drug and to identify potential side effects. It is usually carried out in a small number of healthy individuals (10-80) who do not have the condition for which the treatment is being tested. The medicine is used in low doses initially to test safety and potential side effects, always under careful monitoring and often in a hospital or clinic setting. If initial results suggest that the drug is safe, the dosage may be increased gradually so that researchers can ascertain what a safe and well-tolerated dose might be. For advanced therapies which are particularly invasive, such as stem cell or gene therapies and which may only require a single treatment, phase I may be carried out in people with the condition it aims to treat.
  • Phase II – the treatment is used on a larger group of people (100-300) with the condition it is intended to treat. This is critical for deciding whether or not a treatment is effective enough for it to continue into a larger later stage clinical trial. Based on the results of the phase I study, the optimal doses will be used and known side effects will be monitored in detail. It is important at this stage to define what is meant by the drug being “effective” and discussions will have taken place with both patients and the regulatory authorities to agree on how the drug has a significant clinical benefit.
    Phase II trials are usually designed as ‘double-blind’, which means a number of people (sometimes known as the experimental group) are randomly chosen to follow a course of the active treatment. Another group (known as the control group) is given a recognised, standard therapy or, less commonly in Parkinson’s, a placebo (dummy drug). It is referred to as double-blind because none of those involved – neither the patients who are taking part in the trial, nor doctors and researchers – know who is taking the new treatment and who is in the control group. This means that it is unlikely that their findings can be prejudiced. The duration of a phase II trial will depend on the duration of treatment with the drug. It is not unusual for a phase II trial to last from 2-5 years and this will include both participant recruitment and subsequent data analysis.
  • Phase III – if the phase II results are positive then the study is extended to a much larger group of individuals (1,000-3,000) in the hope that this will reinforce findings and show that initial success in the previous phase was not random. A phase III trial is usually carried out in a number of centres in more than one country and is also usually double-blind. Not all people with Parkinson’s will be suitable for all trials and this will depend on the symptoms which are being targeted. Eligibility to take part is referred to as ”inclusion” and “exclusion” criteria. The results of this phase provide more detailed information on how effective the treatment is, how it compares to treatments already available, and the benefits, risks and optimal dosages. Whatever the format of the trial, volunteers are very closely monitored at all times and tests are carried out, including blood and heart tests. If any safety concerns arise, the trial may be stopped.
    At the end of the agreed testing period which can last from several weeks to several years – the trial is ‘unblinded’ and it is revealed who has been taking the new treatment and who has been following the ‘control’ treatment. Conclusions can then be drawn from the results of this stage of testing. The desirable result is of course that those on the treatment under trial have shown more improvement than those on existing medications.
    Some trials are also ‘open label’ which means that the participants and researchers know what treatment is being taken and there is no ‘blind’ element to the study. However, these are not common for Parkinson’s as the “placebo effect” is particularly strong. Essentially, when a person thinks that they are receiving a beneficial drug, they will show some positive effects, even though there may be no active drug in the tablet that they take. This can last up to six months, so it is important that this is taken into account when designing a Parkinson’s study.
    Even if a new therapy demonstrates benefit in a phase III trial – they have a clinical benefit for specific Parkinson’s symptoms the drugs may not ultimately be available for treatment as they may not be sufficiently more effective than existing therapies.
  • Phase IV - assuming that all previous phases are successfully completed, the drug company will apply to the regulatory authorities for permission to use it as an approved treatment. This process is very detailed and time consuming and can take one to two years to complete, depending on issues raised by the authorities. During the approval process, further data will be collected and additional information may be requested by the regulators. This is particularly important if there is some evidence of harmful side effects. The ultimate decision on whether to grant a license for clinical use is that the benefits of the drug should outweigh any risks that may exist. However, until the treatment has been registered it cannot be made more widely available. Once a drug has been licensed for use in the clinic, it is still monitored for safety. Patients can report adverse or side effects on the EMA website. There may also be similar facilities available at a national level
  • Availability for patients - once a drug has been approved for use by the EMA, this does not mean that it will be available for use in the clinic. A subsequent assessment has to take place at a national level by the Health Technology Assessment (HTA) bodies. In the U.K., this is the National Institute for Health and Clinical Excellence (NICE). While the EMA assesses the efficacy and safety of the medicine, the HTAs assess its cost effectiveness. While a new drug may be more effective than an existing one, this must be balanced with its price. The decision may differ between individual countries, thus explaining why not all drugs are available in all European countries.

Getting involved in Parkinson's clinical trials

There is often a shortage of volunteers to take part in clinical trials. This may be due to a lack of easily available information on trials in a particular location or area, or to doctors being unaware of trials that are being held locally.

If you would like to become involved in a trial, it is essential to discuss this first with your doctor as it is likely that they will be required to refer you to the trial centre. You should find out as much information as possible about the trial so that you can fully discuss your participation. Your doctor will be able to advise you on the advantages and disadvantages for your own particular situation, and they may be able to refer you to other members of the multidisciplinary team who have more knowledge about a particular area of research.

Depending on what the trial is investigating, the research team will be looking for people who fit specific criteria – called inclusion and exclusion criteria (or eligibility criteria) – that ensure you are suitable for the trial. Screening usually involves answering questions about your Parkinson’s, your current medication, treatment history and checking details such as your age and when you were diagnosed. This information is frequently available on the trial website. You may need to have an additional detailed examination which may include blood tests, scans or other clinical assessment tests. If you fit the trial’s eligibility criteria, you may then be invited to take part in the trial.

What are the benefits and risks in participating?

There are many benefits to taking part in a clinical trial. You may feel that by doing so you are playing a more active role in your health as well as helping scientists to develop new medications to help other people with Parkinson’s or move closer to the development of a cure. Participation can also provide opportunities to learn more about Parkinson’s and to meet others in a similar situation. Participants can also play a key role in providing feedback on the trial design and therefore improve the format of future studies.

The safety of participants is always paramount and there are strict codes of practice that must be observed to protect volunteers. Data protection is one key factor and participants’ names and personal details are not usually disclosed unless there is a medical reason to do so. This is covered by the new EU General Data Protection Regulation (GDPR).

However, as with any new treatment, there will always be an element of risk involved, although every care will be taken to eliminate the risk of serious or even life-threatening side effects. The phase I trial of the study is always designed to strictly assess the safety of the medicine and it will be terminated if any significant adverse effects are reported. Any potential side effects identified in phase I will then be carefully monitored and reported on in the later phases.

No assurance can be given when entering into a trial that the treatment will improve your condition and, in some cases, this may deteriorate in the absence of effective medication. It is likely, though, that you would be taken off the trial if your condition were to worsen; this is something you should discuss with your doctor before entering the trial. You should be provided with a patient information sheet which will contain all of this information. You may also experience unwanted side effects or need to undergo tests such as blood tests or scans which you may find unpleasant. Information will be provided before you agree to enter into the trial. Participating in trials can also be time-consuming and may require hospital stays. Trials are required to reimburse reasonable costs incurred, such as travel and accommodation. However, it is unlikely that costs such as time taken off work will be reimbursed. If you are concerned about long term side effects, you should discuss trial insurance with the trial coordinator.

You can withdraw from a trial at any time. If this happens, the care team should be advised of the reasons for withdrawing as this may influence the future recruitment of additional trial participants.

Treatments used in trials may not be made available immediately, or at all, after the end of the trial, in which case you would revert to treatments that are currently available. Even if the new treatment is effective and is brought onto the market, you should be aware that you may not be prescribed it to treat your Parkinson’s. The condition is extremely variable and new drugs are unlikely to be effective for everybody. Furthermore, you should remember that although a new drug may be approved by the EMA, it may not be reimbursed for routine treatment within your own country.

Consent and responsibilities

If you are accepted to join a trial, the research team running it must have your permission (consent) to enter you into the trial. You will be asked to sign a form to show you understand what is involved in taking part and that you agree to this. Before signing, the research team should talk you through what is involved in detail and answer any questions you have. It is important to note that although you will be asked to sign an informed consent document, this is not a contract and you may withdraw from the trial at any time.

Below are just some of the responsibilities you should expect to take on when enrolling as a volunteer. You should:

  • read all the information you have been given and ask questions if anything is unclear
  • ensure that you inform study staff if your contact details change at any time
  • provide a full medical history before you start treatment and a list of any medications you take, including over-the-counter medications
  • keep a written record and report any illnesses or changes in your condition as the study progresses
  • follow instructions carefully and always talk to study staff if you think you need to make any adjustments
  • diarise any appointments you are asked to attend as these are important to the study
  • be honest with your feedback relating to the treatment or study
  • try to remain in the study until its conclusion unless there is good reason to withdraw
  • follow instructions regarding the submission of any expenses, making sure that receipts are passed on within the requested timeframe.

The trial may last for several years so it can take a long time for the results to be known. Once completed, the results will be available to all those who took part.

How do I find the right trial for me? 

There are many trials running at any one time on a range of potential Parkinson’s treatments. Some may run only in a particular country, while others may span many countries. Finding the right trial in your own country will require time and patience so don’t be put off if you don’t find a suitable trial straight away.

A good place to start is by asking your doctor or neurologist if they are aware of any trials or research centres in your area that may be suitable for you. Others you know who have participated in trials before or a local Parkinson’s support group may also have ideas to share with you.

If there is a research centre in your area, try calling the neurology department and ask to speak to someone involved in Parkinson’s trial recruitment.

The list of trials is constantly changing but the following websites may be helpful in researching current trials:

  • The EU Clinical Trials Register provides a search facility for information on clinical trials in European Union (EU) member states and the European Economic Area (EEA)
  • Be Part of Research lists clinical trials based in the UK
  • Parkinson's UK details current UK Parkinson’s clinical studies
  • provides a search facility for trials in over 170 countries on a wide range of conditions
  • Fox Trial Finder lists ongoing Parkinson’s trials and research studies and also matches registrants to the trials that need them and are best-suited to their specific traits
  • CenterWatch includes links to research facilities for patients and healthcare professionals
  • database of primary clinical trials

It is a good idea to record all of the trials and contacts you pursue and the responses you receive. If you enquire about a trial and you are unsuitable or they are no longer recruiting, ask the coordinator to keep in touch regarding future trials which may be more appropriate.  If you are initially unable to join a trial which interests you, don’t be discouraged from enquiring about others as new ones are regularly launched and need a broad range of participants. 

Once you have found a trial you are interested in, check the criteria for participation. If you think you are suitable, contact the trial coordinator and ask for more detailed information and raise any particular queries you have.  If you meet with the trial coordinator, it may be helpful to take someone with you so that they can take notes. 

If the trial is currently enrolling, you may be asked to attend a screening appointment before being accepted. Some medical tests may be performed to establish your fitness for the trial and so that your health before and after the treatment can be compared.

Key information to find out is outlined below.

  • What is the purpose of the trial?
  • How long is the trial expected to last?
  • What tests, if any, have been conducted so far into the efficacy and safety of the treatment? How can I access results of previous investigations?
  • Why do researchers believe that the treatment will be as or more effective than my current treatment?
  • Is there a control or placebo arm in the trial?
  • How many hours will my involvement take and over what period of time?
  • When will I start?
  • Will I be asked to sign any contracts?
  • What are my responsibilities as a participant?
  • How will I know if the treatment is working?
  • Is the treatment likely to make me feel unwell or uncomfortable and if so, for how long?
  • What experimental treatments or tests will be carried out?
  • Where will these be carried out, will hospital stays be required and if so how frequently and for how long?
  • Will I be expected to attend any meetings and if so how many and for how long?
  • Is the treatment likely to have an impact on my daily life and quality of life?
  • Will I be able to take other medications and/or over-the-counter treatments?
  • What are the perceived risks, benefits and possible side effects in comparison to my current treatment?
  • What long term follow up will be required?
  • Who will monitor my treatment, care and safety during the trial?
  • Will someone keep my doctor informed of progress?
  • Is there someone I can contact on the research team if I have any queries?
  • Who will pay for the treatment and will my expenses be reimbursed?
  • If my symptoms improve during the trial, will I be allowed to continue using the new treatment once the trial has ended, and before it is registered?
  • If I become unwell or develop symptoms related to the trial treatment, will I be entitled to medical care and how will this be handled?

Be prepared to keep notes in order to track changes to your symptoms, either using forms provided by the trial coordinator or your own notebook or Parkinson’s diary. Written notes are always helpful for remembering specific details when reporting back to the research team.

Terms commonly used in relation to clinical trials

Control/control group: in a trial the control is usually a group of people who receive a placebo (dummy) instead of the experimental treatment or receive an existing therapy. This group is used as the standard by which to evaluate the benefits of the new therapy.

Double-blind: in a double-blind trial neither the participants nor the researchers know who is receiving the active treatment and who is receiving placebo. This is in contrast to a single-blind trial where the researchers know who is in which group but the participants do not, or an open-label trial in which both participants and researchers know who is receiving the active treatment or placebo.

Eligibility criteria: guidelines to determine who is suitable and able to participate in a particular trial. A study will require that participants share certain criteria, for example gender, age, medical history, to ensure that trial results are due to the treatment under investigation and are not influenced by other factors. This allows for more accurate and meaningful results. 

Inclusion/exclusion criteria: agreed standards used to identify who is suitable for a particular study. These standards also ensure the safety of those who enroll and generally include gender, age, previous treatments received, the stage of a condition and other co-existing medical conditions. 

Informed consent: a document that details the study in very understandable terms. This usually includes the purpose and duration of the study, the proposed treatment, its potential benefits and risks, details of any studies to date, agreed procedures and key contacts. All participants must give their consent based on the information contained in this document. If unable to give consent then someone authorised to act on the volunteer’s behalf must do so. Although this document must be signed, it does not constitute a contract and volunteers can withdraw from a study at any time.

Placebo: a placebo is a pill, liquid or other form of treatment that has no active medication. It is usually used alongside an active form of the treatment or compound being trialled. Use of a placebo against the active treatment allows comparisons to be made on efficacy.

Protocol: a very detailed plan which forms the basis for the conduct of a scientific or medical experiment, treatment, or procedure. A protocol is in place for all clinical trials both to protect the participants and to answer specific research questions. Key points in a protocol include the nature of the participants, the schedule of any procedures or tests, the medications and dosages involved, and the time-span of the study. 

Screening: process for the selection of study participants based on agreed eligibility criteria (see above).

Content last reviewed: November 2018


We would like to thank Dr Kieran Breen, PhD (St. Andrews Healthcare, UK) for his help in reviewing this information.

Related reading

  • Participation of Early Parkinson’s Patients in Clinical Trials Crucial to Finding Cure, Expert Says
  • Navigating Clinical Trials - A Guide for Parkinson’s Patients and Families (The Michael J. Fox Foundation)
  • From lab to patient: how medicines are approved - video produced by the European Medicines Agency (EMA

Articles from Parkinson's Life online magazine

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