Clinical Trial Recruitment 101: How to Recruit Participants for a Study

What is the best way to recruit participants for a study?

There is no simple answer to the question of how to recruit participants for a study in clinical research. The ideal recruitment strategy will depend on the specifics of the trial type and protocol, the capabilities of the sponsor and/or entity conducting the trial, the availability of eligible participants, and certain demographic and behavioral factors of those participants.

This article provides various resources for trial sponsors and clinical researchers to dive deeper into aspects of patient recruitment, and then answer the above question in a way that makes sense for the trial in question and their organization's unique needs.

Ethical considerations in research study recruitment

Before we proceed with answering “how to recruit participants for a study,” let’s do a quick recap of ethical considerations in research recruitment. There are a few important things to keep in mind related to regulatory compliance, ethics, and IRB submissions/approval. Keeping these concepts present through the design of the recruitment plan and during enrollment will make recruitment processes smoother by avoiding unexpected delays due to disapproval of study materials or re-approvals for unforeseen changes to said materials.

So, what are ethical considerations in relation to patient recruitment for clinical research studies? Essentially, the following rules and regulations are put in place to protect patients - in terms of their health and safety, their basic human rights, their data and personal privacy - and to ensure they are treated in an ethical manner (i.e., fairly and humanely) throughout the clinical trial, which begins with their first exposure to the study, be it through their physician or through promotional material. These considerations are provided in a bullet-point list to serve as a global overview that is easy to navigate – more information can be found by following the references provided at the end of the list.

1. All study materials must be approved by an IRB - Anything that will be seen by participants requires IRB approval prior to them seeing it. If modifications are made, a modification application must be submitted. Keep potential delays here in mind, and consider designing alternative versions to allow quick swap-out of pre-approved study materials.

2. Required content for recruitment materials - Recruitment materials generally must contain the following information:

  • Clear indication that it is a research study (and not a therapy, program, etc.)
  • Clear description of the purpose of the research study
  • Basic eligibility criteria (those which a prospect can assess him/herself)
  • Requirements of the participant (timeline, study visits, procedures, etc.)
  • Location (of study sites or indication that it is a remote trial)
  • Regulatory status of the investigational product/drug/device, if applicable
  • Contact information

3. Prohibited content/terminology in recruitment materials - The following are forbidden from being included in recruitment advertisements:

  • Promises of free healthcare or treatment
  • Compensation that is highlighted or otherwise made to stand out from the rest of the text/content
  • Claims that the investigational product is safe, effective, or equivalent to another treatment/product
  • Claims that the trial will lead to health benefits or positive outcomes for the participant
  • Exaggerated allusions to benefits, whether personal or societal
  • Promises of discounts on the investigational product after its approval

4. Voluntary participation - Researchers must take explicit care to avoid coercion and inducements in research. Research participants may not be urged, forced, or coerced to take part in research studies.

5. Respect targeted ad bans and online privacy - Many social media platforms have banned the use of targeted advertising, wherein users’ sensitive personal information is used to target them. Ads not respecting these rules will not be approved. Recruitment outreach and communications must respect the privacy of every individual, and those interactions must not reveal their condition or identity to third parties or the public.

6. Data confidentiality and security - Data collected about potential participants should be treated as confidential, and should be stored appropriately (securely) to avoid data breaches and leaks of personal data that can compromise personal privacy.

7. Clear, direct, and unbiased language - Language should be understandable by the average person (layman terminology), and study objectives and protocol details should be laid out directly and clearly, avoiding misleading statements, coercive wording, and unfounded or exaggerated promises or claims.

8. Circumvent the therapeutic misconception - Study materials should deliberately avoid the “therapeutic misconception,” wherein participants believe that taking part in a study is guaranteed to benefit their health.

9. For further information on these points, please refer to:

Powerful recruitment strategies: From planning to consenting

Our aim with this article is to provide sponsors and researchers with an overview of multiple concepts and considerations that come into play when designing and executing an effective patient recruitment strategy. We all know that recruitment can be a source of costly setbacks. Optimizing recruitment begins well before the recruitment process begins - due consideration of common challenges is necessary in order to understand the target population, promote diversity, and design recruitment strategies that are effective. This includes designing trials that are optimized for recruitment success. After discussing these challenges and considerations for designing recruitment strategies, we will provide further information on specific recruitment methods, including pointing to some powerful recruitment tools to supplement recruitment activities and the options available for outsourcing recruitment to specialists. Finally, we will link to explanatory content that goes into greater depth about various marketing and outreach strategies on different platforms to optimize exposure and speed up enrollment by reaching the right participants.

Importantly, recruitment success begins with designing trials and protocols that are already set up with recruitment success in mind! See our articles on patient centricity and decentralized clinical trials as a starting point. From here on, we will focus on optimizing recruitment, assuming that the trial has been designed in consideration of minimizing patient burden and enhancing participant experience. If that’s not the case, the following tips will still be entirely useful - but keep these concepts in mind for future trial designs, as patient centricity is slowly but surely becoming the norm rather than the exception in the clinical research industry.

Have a look through the following sections, which we have conveniently split up into three broad stages/concepts to help you pick and choose the guidance that is pertinent to the aspect of recruitment you’re looking to improve.

A. Background information to guide the design of a recruitment strategy

Recruitment challenges, eligibility criteria and screening, diversity and underserved populations

Recruiting into research studies is a complex undertaking. It requires a thorough understanding of your target population, including a clear definition of eligibility criteria for the trial, and it’s really useful to understand some of the (unfortunately, very) common issues that clinical researchers face in recruiting and enrolling a sufficient number of eligible participants on time.

Now, back to the design of the recruitment plan. To begin, check out the following resources to gain a deeper understanding of the clinical research recruitment landscape and common challenges encountered. This information is powerful for enabling you to turn these challenges into insights in order to come up with ways to address them and prevent them from becoming problematic.

Next, let’s consider the eligibility criteria. Nearly every trial has them, as these constraints act to encourage some degree of homogeneity in the sample, which in turn improves statistical power. In other words, constraining the sample allows researchers to control for certain covariates and prognostic factors, at least to some degree. These can include basic demographic factors such as biological sex and age, or extend to extremely specific criteria such as narrow ranges on a certain clinical parameter (hypothetical example: average systolic blood pressure of between 100 and 110 mmHg over the last 6 months). The trade-off is that strict eligibility criteria limit the pool of potential participants, and results obtained from very narrowly defined subsamples of the general population are less likely to be generalizable to the broader population. For extremely rare diseases, it makes more sense to use broader eligibility criteria so as not to unrealistically limit the sampling pool, and further since the rare condition is already a highly specific criterion. Eligibility criteria are also put in place as a safeguard against exposing high-risk patients to drugs or interventions that may be particularly risky for them.

Clinical researchers should aim to strike a balance between accessibility (to a sufficient participant pool for researchers, and fair accessibility to the study for diverse populations) and statistical power, and keep generalizability of results and the representativeness of the sample in mind. Check out the articles below to dive deeper into defining appropriate eligibility criteria and the factors involved in the decision:

The final consideration we want to touch upon in the context of planning and designing effective recruiting strategies is diversity in trial participation. This has become an important topic over the past years, as it has become evident that many minority groups and communities are (sometimes significantly) under-represented in clinical research studies. Diversity and inclusivity in clinical trials are important for multiple reasons. First, there are genetic differences amongst the broader population which can have significant impacts on how individuals respond to treatments - ensuring inclusion of diverse populations improves the representativeness of the study sample, and increases the likelihood that results can be generalized. Further, this helps monitor, to some extent, for potentially dangerous responses to a given treatment in certain groups, which may not have been identified in a sample that did not represent those groups. Second, the under-representation of certain groups can be a reflection of the reality of unequal access to healthcare and potentially beneficial novel treatments in certain communities. Not only is this a discrepancy that should be rectified for the sake of fairness and ethics, but increasing awareness and rapport in these communities can work toward dispelling negative perceptions and misconceptions that may act as confounding factors toward the lack of involvement. Check out the following article and the FDA guidance for more info:

B. Recruitment methods and tools

Recruiting methods, powerful recruitment tools, and outsourcing

Now, let’s get to directly answering the question originally posed: How to recruit participants for a study.

The first topic here is pre-screening. Pre-screening is an invaluable step for narrowing down interested participants to high-interest/high-eligibility candidates, preventing costly screen failures down the line. In many cases, pre-screening can be set up and then function passively, greatly reducing the workload on sites and investigators. At Power, our speciality is matching patients with relevant clinical trials, which is powered by our patient-friendly platform. The powerful pre-screening feature serves a double purpose in that prospects’ answers to sponsor-defined pre-screening questions are used to create a database of high-interest participants, which makes it extremely easy for sponsors to reach out to further them through the recruitment funnel. If you’re recruiting for a study, reach out to us and verify your trial on our platform with a streamlined pre-screening feature. Check out the following link for more information on pre-screening and screening:

In terms of executing the recruitment and outreach strategies, there are various ways to go about it. The following links will bring you to great resources outlining specific recruitment methods, focused on patient-centric recruiting strategies and tools that can help you succeed in recruitment. Have a read through; we’re sure you’ll find something that helps you design the best recruiting strategies possible for your trials:

If all of this seems like simply too much to take on - this is often the case for smaller organizations - there may be real value in considering outsourcing recruitment efforts to specialists in clinical research recruitment. These could be a dedicated clinical research recruiter, or CROs or other providers who offer recruitment services and bring their own site and patient databases to the table, amongst other operational services and technological solutions:

C. Clinical trial marketing and outreach campaigns

Guidance for digital marketing campaigns on social media, Google, and Facebook

In today’s clinical research industry, which is more connected than ever before yet still suffers from poor recruitment statistics, trial recruitment specialists and sponsors have turned to marketing tactics to expand exposure to their trials. Capturing the attention of people, who are bombarded by advertisements on a daily basis - an estimated 4,000 to 10,000 per day, in fact - is increasingly difficult (and that statistic is from a few years ago already!). Thus, there is a lot of value in leveraging marketing techniques to increase exposure of your trial. As a starting point, have a look through our introductory article on the topic of clinical trial marketing:

When it comes down to specifics, things can begin to look quite complex. Different social media platforms with differing user demographics, different ad types, and distinct rules and regulations, combined with the fast-paced nature of social media and digital marketing, highlights the potential value in partnering with a digital marketing expert. However, with some dedication and time, it’s not all that hard to navigate these platforms and design and launch highly effective recruitment campaigns on social media.

We recommend first reading through the concise and helpful “Use of Social Media” section of this guidance published by the Iowa State University Institutional Review Board, which serves as a checklist to ensure that you have the appropriate perspective and awareness of pertinent issues when going into this area. Relatedly, our overview piece on social media recruitment goes into depth on important considerations for patient privacy, targeting methods in light of targeted ad bans, common challenges and potential solutions in social media recruitment, designing and monitoring a recruitment campaign, and gives an introduction to the major platforms and their specific ad campaign types:

If you’re interested, take a look at more detailed guidelines for two of the major online marketing channels that have proven to be extremely effective for many clinical trials: Facebook and Google.


We hope that this global overview of important considerations, challenges, and methods of recruitment has been useful, and that you can walk away with some helpful information for how your organization or trial team might go about deciding how to recruit participants for a study. There are a lot of options for patient recruitment, but perhaps the most important aspect of recruiting into research studies that we would like to highlight is the benefit of proper prior research and planning. Past trials offer extensive insight into what has and has not worked, either in your organization or for trials of a similar nature, and taking time to define and then understand your target population - their needs, their struggles, and where they are most active - will go a long way in optimizing your recruitment efforts. Bring patient experience and recruitment success to the table early on, in trial design and protocol development, to set the study up for successful and quick recruitment from the get-go. Whatever strategies and tips you decide to adopt, keep regulatory compliance and IRB approval in mind, and remember that recruitment is a skill. Especially in these times of extreme connectivity and exposure to advertisements, learning to reach your target participants with messages that resonate with them is an art, which you can only improve upon with each trial and each iterative effort.