Empty chairs - 7 Reasons your Clinical Trial isn't recruiting enough patients

by Anemone Rutter • 21. 08. 2019

7 Reasons your Clinical Trial isn’t recruiting enough patients

As many as 85% of clinical trials fail to recruit and retain enough patients in order to meet their enrollment timeline. In total, 80% of trials fail to finish on time, despite the fact that a good third of a study budget often goes into patient recruitment and retention. (1)

50% of sites enroll one or no patients in their study, meanwhile studies show that only 3% of cancer patients are even aware of opportunities to take part in a clinical trial. (2) Sponsors and clinical research organizations are finding it increasingly difficult to attract and retain the required number of patients for studies, which leads to a costlier clinical trial, lower staff morale and less statistical power for the study and the validity of the results. Here are 7 potential reasons why studies are not recruiting enough patients:


1. Site selection

A commonly overlooked problem, a site must fulfill the criteria needed to meet the enrollment targets. This includes an Investigator with experience in similar trials (or trials in general) and motivation to recruit enough patients, as well as experienced study staff that is aware of the administrative hurdles of clinical trials, such as sub-investigators, a study nurse or a trial coordinator. Often Investigators underestimate the workload involved in clinical trials and, due to lack of time, neglect the responsibilities of recruitment. Another factor may be that they are involved in other clinical trials at the same time, which might be of greater interest or offer more attractive incentives.

2. Over-estimation by investigators

This leads right into the next problem, the over-estimation of Investigators of how many patients will realistically be included in the trial. It is important to understand how large the corresponding patient population is, how many people are needed from this population and how many will actually participate. This is where many Investigators over-estimate the number of patients they will ultimate include in the trial. (3)

3. Overly restrictive inclusion criteria

While inclusion and exclusion criteria are very important for the validity and reliability of trials, if too tight, potential willing patients will be turned away, despite otherwise fulfilling the basic criteria for the trial. Here it is important to outweigh the risks and benefits of widening the inclusion criteria.

4. Patients´ lack of awareness

Educating potential patients about a study is integral to successful recruitment. Often, patients with a disease, which a study is investigating, are not informed about it by their physician. Furthermore, patients may be reluctant to enter a trial if it is not directly recommended by their own physician. Studies show that patients with a higher level of education are more likely to consent to a clinical trial, whereas social circumstances, language barriers and cultural differences can act as barriers to recruitment due to lack of information and mistrust towards western medicine. (4) One way to improve awareness could be for the sponsor or clinical trial companies to market the study correctly and help build awareness towards patients of the trial through leaflets, advertisement etc.

5. Paperwork for patients

Patients can be overwhelmed when faced with having to keep a diary for multiple months or filling out pages and pages of questionnaires. A study can easily become very time consuming for patients, especially if they have restrictions (e.g. Alzheimer´s disease, elderly, and children) and need a second person to help them with the paperwork. This can definitely influence the number of drop-outs in a trial. Alone the informed consent form is often 30 pages long and can be very overwhelming for many patients.

6. Effort for patients

This leads into the next issue, which is the effort that a patient must put in for the study, in the form of multiple visits to their doctor. This is often associated with long waiting times, and many patients must also bring a carer along to these visits (again, children or elderly persons). Many people live far away from the study site or have a full-time job they cannot leave for the frequent study visits. Furthermore, participants are subject to regular invasive medical testing, e.g. blood sampling, urine samples, MRI and CT scans.

7. Chance of receiving placebo

With most studies administering a placebo treatment to a third or up to 50% of the total participants, many patients fear of falling into this group and not receiving treatment for their illness. (5) If faced with the choice of receiving the current standard treatment for an illness or having a 50% chance of receiving a different treatment, but also a 50% chance of receiving a placebo treatment, they would rather be safe and receive the standard treatment.

What we can do at ZAK to reduce these hurdles

As a CRO, we do not have an influence on most of the problems mentioned above.

  • The study protocol is predefined by the sponsor, who has thought about what data he would like to collect and how he would like to collect it. Since clinical trials can cost an enormous sum of money, data should be collected in the most efficient way possible.
  • Doctors have different motivations when it comes to participating in a trial and therefore show varying degrees of engagement. The appeal of a new drug plays an important part. Drugs that are new and promising spark great interest and motivate more doctors to participate in a trial; whereas doctors that only participate in order to be able to economize having study staff usually show less interest in trials.
  • The motivation of patients is also variable. Patients who are happy with their current treatment are not eager to stop taking their trusty medication in order to try a new drug whose efficacy hasn’t been explicitly proven and with risks that are not fully understood yet.


Different interests and motives clash together within clinical trials. We at ZAK work hard to be available as a point of contact. Through our personal dedication and commitment, we are able to coordinate any measures necessary and find individual solutions to these problems.

Within discussions prior to a clinical trial (feasibility and pre-trial visits) we strive to have a good dialogue with the study doctors and to brief them well before any possible issues arise later on, e.g. to avoid problems with recruitment due to over-estimation or lack of information.

As an interface of clinical trials, we see ourselves as mediators between these different positions and interests.

If you would like help with a project, please do not hesitate to contact us per telephone: +43-1-879-38-95 or per email under the following address: office@zak-services.com.


(1) https://www.clintec.com/services/patient-recruitment-retention/
(2) http://www.medelis.com/why-oncology-studies-finish-late-and-over-budget/
(3) https://www.biotaware.com/blog/why-patient-recruitment-clinical-trial-such-challenge-8-major-reasons-why/
(4) http://www.appliedclinicaltrialsonline.com/subject-recruitment-and-retention-barriers-success
(5) https://social.eyeforpharma.com/clinical/5-tips-how-facilitate-clinical-trial-recruitment

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Anemone Rutter

Office Assistant/Medical Student


+43 1 879 38 95

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