What Is a CRO? Understanding Contract Research Organisations

A Contract Research Organisation, or Clinical Research Organisation, is a specialist organisation contracted by a sponsor to perform one or more trial-related duties and functions on their behalf. This definition comes directly from the International Council on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH), whose E6(R2) guideline on Good Clinical Practice (GCP) sets out the framework governing how CROs and sponsors work together.

In practice, the role of a CRO extends well beyond a contractual arrangement with clinical trials sitting at the intersection of science, medicine, regulation and operations and the challenges that arise, such as unclear regulatory pathways, sites operating over capacity, harder-than-expected patient access or protocol feasibility problems. These are rarely foreseeable from a protocol alone and that is one of the main reasons CROs have become such an important part of modern clinical development.

Why CROs are used in clinical research

Clinical development demands a level of infrastructure, specialist knowledge and regulatory experience that is not always practical to maintain fully in-house. This is particularly true for small and mid-size sponsors, from biotechnology companies, medtech organisations, academic groups to charities, but it can also apply to larger pharmaceutical sponsors who need additional capacity or specialist expertise in a particular area.

Under ICH E6(R2), a sponsor may transfer any or all trial-related duties and functions to a CRO, but the ultimate responsibility for the quality and integrity of trial data always remains with the sponsor. Any functions transferred must be specified in writing, and the sponsor retains oversight obligations throughout. This distinction is important: outsourcing to a CRO does not mean handing over accountability.

The value of a good CRO lies in how it brings together the moving parts of a trial, advising on study feasibility, preparing Clinical Trial Authorisation (CTA) or Investigational New Drug (IND) applications, coordinating investigational sites, supporting safety management and ensuring that final reporting reflects what actually happened during the study.

What does a Contract Research Organisation do?

CRO services vary widely depending on the organisation’s size, structure and focus, with some CROs that act as full-service providers capable of managing every phase of a clinical trial while others specialise in a narrower set of functions. In broad terms, CRO activities typically span:

Study start-up

Protocol development, study feasibility assessment, site identification and evaluation, ethics committee and Institutional Review Board (IRB) submissions, regulatory authority applications (including CTAs with the Medicines and Healthcare Regulatory Agency or European Medicines Agency, and IND submissions to the FDA) and site initiation.

Trial delivery

Clinical trial monitoring (including risk-based monitoring approaches), project management, site management, patient recruitment support, pharmacovigilance and Serious Adverse Event (SAE) and Suspected Unexpected Serious Adverse Reaction (SUSAR) reporting.

Data and reporting

Clinical data management, electronic data capture (EDC) system oversight, biostatistics, medical writing and preparation of the Clinical Study Report (CSR) for regulatory submission.

Post-marketing and close-out

Post-approval pharmacovigilance, end-of-trial notifications and trial close-out activities.

Some sponsors engage a CRO under a full-service model, where the CRO coordinates the entire programme. Others use a Functional Service Provider (FSP) model, embedding CRO staff within specific sponsor functions for a particular study or period.

CROs and their role in different clinical trial phases

CRO involvement can span all four phases of clinical development:

Phase I trials are typically first-in-human studies conducted in small populations (often 12–50 healthy volunteers or patients) to evaluate safety, tolerability, pharmacokinetics and dosing.
Phase II trials test safety and initial efficacy in a patient population (usually 200–500 participants) afflicted with the target disease or condition.
Phase III trials are larger-scale confirmatory studies (often 500–5,000 or more participants) designed to generate the evidence needed for regulatory approval.
Phase IV studies occur post-approval and may include post-marketing surveillance, comparative effectiveness research or exploration of additional indications.

Most CROs with clinical operations capability can support Phase II–IV trials. Those with early-phase units or specialist expertise may also support Phase I. PHARMExcel’s focus is primarily on Phase I-IV clinical trials, where our work covers study management, monitoring, regulatory affairs, safety oversight and clinical writing.

Why sponsors choose different types of CRO

Not all sponsors need the same kind of CRO, and not all CROs are designed to solve the same problems.

Some programmes require the scale and global infrastructure of a large CRO, particularly highly multinational trials involving complex internal systems and large site networks. In other situations, a smaller specialist CRO is a better fit. This is often the case when sponsors need closer oversight, more continuity of team, more direct communication and fewer handovers across the life of the study.

This distinction matters in practice. Large CROs can bring scale and reach, but they can also introduce more layers of communication and less day-to-day visibility for the sponsor. Smaller CROs (like PHARMExcel) often work with more flexibility. This is because teams are closer together, and there is usually more continuity between feasibility, study start-up, active delivery and close-out. For many sponsors, particularly those running complex or high-priority studies in specialised therapeutic areas, that continuity represents a genuine operational advantage.

How CROs support regulatory compliance

Regulatory compliance sits at the centre of every clinical trial. Studies cannot start without the appropriate approvals in place, and they cannot continue properly unless amendments, safety reporting and ongoing interactions with regulatory authorities are managed correctly.

CROs often help sponsors prepare and coordinate the submissions needed to run a trial. Depending on the geography and the CRO’s remit, this may include Clinical Trial Authorisation (CTA) applications to the MHRA or EMA in the UK and Europe, Investigational New Drug (IND) submissions to the FDA in the United States, ethics committee applications, protocol amendments, annual progress reports and end-of-trial notifications.

Beyond document preparation, effective regulatory support requires an integrated understanding of how regulatory activity connects to the operational life of the study. Submissions that are disconnected from site realities, safety oversight or project timelines create problems that tend to surface at the worst possible time. The strongest CROs treat regulatory work as part of the clinical programme, not as a separate administrative stream managed in parallel.

How to choose the right CRO partner

Selecting the right CRO is one of the most consequential decisions a sponsor makes when initiating a trial. Some useful questions to consider:

Does the CRO have relevant therapeutic and regulatory experience? Experience in your therapeutic area and in the geographies where the trial will run is not interchangeable with general capability. Ask for specific examples.
How is the team structured, and who will actually work on your study? In larger CROs, the team presented at bid defence and the team that delivers the work can differ significantly. Understand who owns day-to-day delivery and what staff turnover looks like.
Is the CRO’s regulatory capability integrated with its operational delivery? Regulatory and operational work that runs as separate streams creates risk. Ask how feasibility, start-up and active monitoring are coordinated internally.
What does the CRO’s quality system look like? CROs should operate under a documented quality management system consistent with GCP requirements. Ask how they handle protocol deviations, audit findings and corrective actions.
Is the CRO a vendor or a genuine partner? The best CRO relationships involve genuine collaboration, clear communication, proactive problem-solving and a team that understands the sponsor’s goals, not just their task list.

CROs and the increasing complexity of modern trials

The role of CROs has expanded as clinical trials have become more specialised. Studies today are more likely to involve narrow patient populations, biomarker-led inclusion and exclusion criteria, complex eligibility requirements, intensive follow-up schedules, decentralised or hybrid delivery models and heightened expectations around data quality and regulatory oversight.

This means sponsors are increasingly looking for more than additional capacity. They need partners who understand how a trial becomes difficult in practice, not just how it was intended to run at the protocol stage, and who can identify and manage those challenges before they affect timelines or data integrity.

What this looks like at PHARMExcel

At PHARMExcel, we see the role of a CRO in practical terms. Our work is to help sponsors take a well-designed study and deliver it as a well-run clinical trial, with the right governance, oversight, regulatory management and operational discipline from start to finish.

We are a smaller, specialist CRO based in the UK, supporting organisations across the UK, Europe, Asia, Canada and the United States. Our team brings senior-level involvement across all stages of a study, from feasibility and regulatory planning through to monitoring, pharmacovigilance, clinical data management and clinical writing. We work primarily across Phase I–IV l trials (interventional and non-interventional) and with sponsors who value continuity, responsiveness and direct access to experienced practitioners rather than layers of account management.

One of the practical advantages of a more specialist model is that it avoids the fragmentation that can affect delivery in larger organisations. At PHARMExcel, feasibility, study set-up and active delivery are managed as a connected programme, not as separate workstreams handed between different teams. That means fewer gaps, clearer accountability and a delivery model grounded in how trials actually run, not just how they are planned.

Frequently asked questions about CROs

What is the difference between a CRO and a sponsor?

A sponsor is the company or institution that initiates, manages and takes responsibility for a clinical trial. The sponsor owns the investigational product and is ultimately accountable for the quality and integrity of the trial data. A CRO is contracted by the sponsor to carry out specific trial-related functions on their behalf. Under ICH E6(R2), any responsibilities transferred to a CRO must be specified in writing, but the sponsor retains oversight and ultimate accountability throughout.

What does GCP mean in the context of CRO work?

Good Clinical Practice (GCP) is an international ethical and scientific quality standard for designing, conducting, recording and reporting clinical trials. The key guidance document is ICH E6(R2), which sets out the responsibilities of both sponsors and CROs. Compliance with GCP is a regulatory requirement for clinical trials involving investigational medicinal products in the UK (MHRA), Europe (EMA) and the United States (FDA), among other jurisdictions. CROs working to GCP standards must operate under documented quality systems and are subject to regulatory inspection.

What is the difference between a full-service CRO and an FSP model?

A full-service CRO manages the clinical trial across all functions, from start-up through close-out, acting as a single delivery partner for the sponsor. A Functional Service Provider (FSP) model involves the CRO providing staff or expertise in specific functions only (for example, monitoring, data management or regulatory affairs), with the sponsor retaining management of other aspects in-house. Many CROs, including PHARMExcel, can support either model depending on the sponsor’s needs.

Final thoughts

A CRO is often described as a company that helps sponsors run clinical trials. That definition is accurate, but it only covers part of the picture. The right CRO helps ensure that a study is deliverable, compliant and credible in the real-world settings where it will actually run, accounting for regulatory requirements, site realities and the operational complexity that no protocol can fully anticipate.

For sponsors, the more useful question is not only what a CRO is, but what kind of CRO they need. In a research environment that is becoming more demanding, more regulated and more operationally complex, that distinction deserves careful thought.

Find out more about how PHARMExcel supports Phase I-IV clinical trials, from study start-up and regulatory affairs through to monitoring and close-out. Explore our services