About Us | Parexel London

What is a
Clinical Trial & more About Us

What is a Clinical Trial?

Medications must be reviewed and approved by Regulatory Agencies Worldwide. Before a new medicine can be approved for use in humans, it is necessary to confirm that it is acceptably safe and effective. This is done by carrying out clinical trials such as those on our website.

In these clinical trials, volunteers are given medicines that are being tested or a placebo (a placebo is a ‘dummy treatment’ that looks like the study drug but has no active ingredients), whilst being evaluated by trial doctors and staff members. Once the clinical trials are complete the data is submitted to the regulatory agencies worldwide, which then decides whether the medicine is ready to be released to the public.

  • purple arrowsWhy we do Clinical Trials

In our London Clinic based in Harrow, North-West London, we conduct Early clinical trials. At our clinic, we test new medicines and treatments. They will not have a name and it will not be licensed, meaning not yet approved for sale or prescription anywhere.

Most of our clinical trials are conducted in healthy individuals aged between 18-55 years, though we sometimes need patients with a certain illness.

It is necessary to confirm if a medicine is safe and effective in the human body. The main purpose of testing in an Early trial is to see how the body absorbs, breaks down, distributes through the body, and gets rid of the treatment.

Sometimes, if the medicine is being developed for elderly patients, we will want to investigate the effect increased age might have on these processes by giving the investigational medicine to elderly people, usually between 60 and 85 years.

Occasionally, we want to discover if processes are possibly altered by food by giving the investigational medicine during the presence and absence of meals, we call this a ‘Food Effect’ clinical trial.

Once the Early Phase clinical trial is complete, we aim to understand the safe dose range and potential side effects of the treatment, how it is dealt with by the body and whether it might work in patients.

All our clinical trials are conducted according to Good Clinical Practice (GCP). GCP is a set of recognised ethical and scientific rules that must be followed when designing, conducting, recording, and reporting clinical trials. All our staff are highly trained and work under experienced doctors to perform our clinical trials, and we are regularly audited by the Government’s Medicine & Healthcare products Regulatory Agency (MHRA).

Within our clinical trial site, we have lots of staff including doctors, nurses, research assistants, laboratory technicians, pharmacists, and supporting staff, and we’re very proud of our contribution to advancing modern medicine, improving or even saving the lives of patients for decades to come.

Find out what some of our volunteers have to say about us.

  • purple arrowsWhy we do Clinical Trials

We are based within the grounds of Northwick Park Hospital, Harrow, in North-West London, (we are not part of the NHS). We have our own private wards, with a total of 45 beds.

Parexel is one of the largest global Contract Research Organisations (CRO) in the world. Our London clinic is inspected by and accredited by the Medicines and Healthcare Regulatory Agency (MHRA).

Most of our clinical trials need some overnight stays so we have a pleasant and welcoming environment for our clinical trial volunteers. Our facilities include a comfortable volunteers’ lounge, with a TV area (including SKY Sports), some games consoles, a quiet reading area, there is also access to online computers and for those volunteers who prefer to bring their own devices, there are a limited number of sockets available. We encourage our volunteers to bring their own headphones, to minimise disruption to others. Volunteers also have access to a large and spacious dining room, meals are prepared and served on-site.

There are also dedicated procedure rooms, as some of our clinical trials require specific specialised tests. We are very experienced within the areas of the chest, eyes, skin, and nervous system.

  • Parexel Early Phase Clinical Unit
  • *Click on each room to view an image

Verification Area


COVID-19 Test Area


Consenting Ward


Screening Ward


Physician Assessment Area



Screening Area

  • Verification Area
  • COVID-19 Test Area
  • Consenting Ward
  • Screening Ward
  • Physician Assessment Area
  • Laboratory

*Floor plans not to scale


Reception Area










Volunteers Lounge


Nurse Station




EEG Cubicles


Respiratory Chamber


Shower Block & Toilets





Clinic Area

  • Reception Area
  • Wards
  • Volunteers Lounge
  • Nurse Station
  • Kitchen
  • EEG Cubicles
  • Respiratory Chamber
  • Shower Block & Toilets
  • Laboratory
  • Pharmacy
  • green arrowsCOVID-19

Throughout the pandemic, we have a COVID-19 Response Plan in place which defines the processes and responsibilities related to the prevention of a COVID-19 outbreak at our clinic as well as the detection and management of potential/confirmed COVID-19 infection. Our staff and volunteers are provided with PPE, symptom monitoring, sanitisation, and more.

As part of our Covid-19 measures we are reaching out to all our volunteers a day before their screening appointment to ask:

1. Have you been unwell with flu symptoms or been in contact with anyone with corona virus or flu symptoms in the past 2 weeks?
2. Have you travelled from abroad in the last 2 weeks?

If you answer YES to Q1 do not attend.

If you answer YES to Q2 please advise us of the date and countries visited and do not attend until we provide confirmation.

  • What is a ‘Screening’? What happens at this visit?

When you have spoken to one of our clinical trial recruitment specialists and you’ve answered some initial questions about your health status, gender, date of birth, and other general information, if you’re still interested and suitable to be screened for a study, you will be invited to a screening appointment.

As part of your invitation, we will send you more detailed information about the clinical trial, also including a copy of an ‘Informed Consent Document (ICD)’. This will provide you with ample time to read through it before your screening appointment.

Your screening appointment will be for a specific clinical trial, as each trial will have its own standards and we need to be sure that you fit the standards for the clinical trial you screen for.

Screening Visit:

We will ask you to bring some Identification documents with you, this will be detailed in your screening invitation. During your screening visit, you will have time with our medical and clinical team, you’ll have an opportunity to ask any questions you may have. If you still want to take part, you’ll be asked to sign an Informed Consent Document, before any eligibility assessments and procedures are performed, these do vary from clinical trial to clinical trial, however, an example of these can include:

  • Details of your medical history, including all medications that you’ve taken recently, and any you are currently taking.
  • A physical examination will be performed, you will be weighed, and your height measured. Your body mass index (BMI) will be calculated and one of the doctors will examine you.
  • Vital signs including blood pressure and heart rate will be measured.
  • Breathing rate and body temperature will be determined.
  • An ECG (recording of your heart’s electrical activity) will be performed.
  • Blood samples will be collected for routine safety tests. You may also be screened for hepatitis A, hepatitis B, hepatitis C (viruses that cause inflammation of the liver), and HIV antibodies (the virus that causes AIDS).
  • Blood samples are collected to ensure that you are healthy. Hormone levels in women may be measured and a pregnancy test (beta human chorionic gonadotropin) will be performed.
  • You will also provide urine samples. This will be used for routine safety tests, as well as a test for alcohol and drugs-of-abuse (including cannabis, amphetamines, barbiturates, benzodiazepines, cocaine, opiates, etc.).
  • Review of how you are feeling (whether you feel okay, different from normal or unwell).

A typical screening appointment visit can last up to 4 hours. Study doctors and staff members will go over all tests and assessments. You will be encouraged to ask questions about anything you don’t understand.

Because you are giving up time to attend a screening visit, we will compensate you for your time, details of which will be discussed with you before booking a screening appointment.

A member of our team will update you once all the test results are available to inform you if you are suitable; at this point, if you are still interested in taking part in the clinical trial, we will discuss the next steps.

  • purple arrowsWhat is a ‘Admission’? What happens at this visit?

An admission is a term we use to describe the next step of the clinical trial after screening. If all your screening results are satisfactory and you’re eligible to take part in the clinical trial, you may be invited for admission, to take part in the clinical trial. We will contact you, to confirm whether you want to proceed to this next phase of the clinical trial.

Your personal safety during the clinical trial is of primary importance to us. It is also important that we meet the requirements of the protocol (clinical trial plan). To ensure your safety we will need to check certain things when you are admitted to the Unit as well as during the clinical trial.

Our clinical trials vary in their design, some have a few overnight stays, whilst others have many overnight stays: the number and frequency of follow-up visits can vary from trial to trial. All overnight stay and follow-up visit dates would have been provided to you when you were invited to your screening appointment.


As your safety is of primary importance, we will perform some assessments and procedures on the day you arrive; these typically consist of:

  • Your suitability will be re-assessed.
  • A doctor will take a full medical history, including all medications that you have taken recently, and you are currently taking.
  • A physical examination will be performed (including the measurement of your weight). Your BMI will be calculated.
  • Vital signs including blood pressure and heart rate will be measured.
  • Breathing rate and body temperature will be determined.
  • An ECG will be performed.
  • Blood samples will be collected for routine safety tests. Women will also have a blood sample collected for a pregnancy test.
  • You will provide a urine sample that will be tested to ensure that you have complied with the clinical trial restrictions (avoidance of alcohol/recreational drugs, etc.).
  • Urine samples for routine safety tests will be collected.
  • Review of how you are feeling (whether you feel okay, different from normal or unwell).

Usually, after the results of the suitability re-assessment are confirmed to meet the clinical trial requirements, the next day (day1), you will be dosed with the treatment.

Once dosing has been completed, you will have more assessments and procedures performed and you will remain in the unit for the number of days needed by the clinical study design.

If the doctor is satisfied that you are in good health and that there are no safety concerns, you will be discharged from the Unit after all assessments have been completed for each treatment period.

There is limited space available for you to bring some personal belongings and spare clothing with you. During your stay, there will be times when you are required to remain in your ward, this is typically when procedures are scheduled to be performed, otherwise, you can relax in some of the communal areas of the clinical unit.

The food and beverages you have during the clinical trial are also an important factor in ensuring your safety and well-being during the clinical trial as certain foodstuffs may interact with the trial medication. It is therefore important that you stick to the diet that will be provided to you at the Unit. You are not allowed to bring extra foods with you, whilst on the clinical trial, we will provide all your foods and beverages throughout your stay.

Our clinical and medical teams are constantly available and are highly trained to take care of you during your stay.

  • What is an ‘Follow-up visit and Discharge’? What happens at this visit?

During taking part in a clinical trial there will be appointments for follow-up visits, these dates and times are provided to you during recruitment and again during your in-house stay, you are expected to be available to attend the follow-up and final trial visit dates, punctuality is important for these visits, as the time of the visit is determined by your dosing time.

Typical follow-up visit duration is approximately 1hr, the assessments are usually very similar to the screening assessments. The assessment schedule is detailed in the Informed Consent Document.

If the doctor is satisfied that you are in good health and that there are no safety concerns, you will be discharged from the clinical trial once all your results have been reviewed.

  • Refer a Friend

Do you know someone who may be interested in participating in one of our clinical trials, if so ask them to call us at 0808 134 6555. If you have participated in a study at our unit and they go on to complete a trial, we will give you £150* as a sign of our appreciation. 

*Compensation only for registered volunteers who have completed a clinical trial.