We’ll say it again: terminology can easily become a barrier between patients and the world of clinical trials. It seems that sometimes we take for granted the understanding of what different medical research terms mean and don’t go as in-depth as we probably should.

We have a series of posts exploring questions, practices, and procedures as they relate to clinical trials. Things as basic as how an idea goes from a spark of ‘what if’ in a researcher’s mind to a sponsored clinical trial are among the topics we’ve already talked about here on the blog. We have also answered some of the most commonly asked questions and addressed your financial concerns.

Today, however, we take it a notch further by composing a dictionary of clinical trial terms that will no doubt come in handy when you start searching for a clinical trial on FindMeCure.


Arm – an arm in a clinical trial is a group of participants that have been administered a certain treatment, whether the investigational drug or procedure, an established treatment to compare the new one against or a placebo (‘sugar pill’).

Adverse event – an unfavorable change in the condition of a participant in a clinical trial that becomes evident during the trial or after the trial has ended; it can be a direct result of the investigational treatment or associated with it.  

Allocation – refers to the way participants are assigned to one or the other arm of a clinical trial; allocation can be randomized or nonrandomized.

Blinding – also called ‘masking’ is when one or more of the parties participating in the clinical research study are unaware which arm receives which treatment and it’s done in order to avoid bias; it’s usually patients who are blinded but the research team can be blinded as well – when both patients and researchers are blinded, the trial is called ‘double-blind’.

Clinical study/trial – there is a subtle difference between ‘study’ and ‘trial’, though they’re often used interchangeably; clinical study mostly refers to research done with no interventions, which aims simply to expand medical knowledge; clinical trial, on the other hand, suggests at least some form of intervention, usually aimed at treatment.

Collaborator – an organization that provides additional support to the study, whether financial or otherwise related to the way the study is conducted

Cross-over assignment – refers to how research is structured if participants receive more than one intervention during the full course of the study; for example, if there are two groups of participants and two drugs, in the initial phase of the trial group 1 receives drug A and group 2 receives drug B, then in the following phase group 1 receives drug B and group 2 receives drug A, so they ‘cross over’.

Early phase I – formerly referred to as Phase 0, it involves very limited human exposure and its main aim is to explore how a certain drug affects the body; there is no therapeutic purpose to it.

Eligibility criteria – a set of criteria that may include age, sex, health condition, even socio-economic background, used to include certain populations and exclude others based on the purpose of the research; for example, some studies accept healthy volunteers while other studies do not.

Enrollment – can refer both to the number of participants in the clinical trial or the process of enrollment itself.

Expanded access – also called ‘compassionate use’ is when a treatment in development is used to treat a disease outside of the clinical trial (usually on people who are not eligible to enroll) because there is no better alternative and it’s estimated that the benefits outweigh the risks.

Experimental arm – this is the arm of the trial that receives the investigational treatment.

Human subjects protection review board – also referred to as an ‘ethics committee’ this a board of people who review, approve and monitor the clinical trial protocol in order to protect the rights of the participants.

Informed consent – a process in which patients are informed about the potential risks of participating in the clinical trial, as well as the procedures and interventions they can anticipate if they choose to enroll.

Intervention – any and every action that is the main focus of the trial; intervention can and often does mean treatment, it can refer to the use of a drug or procedure – whether investigational or established, or it can address other forms of ‘intervening’ such as educating participants on a certain issue, introducing a change in their diet or lifestyle and so on.

Investigator – a researcher involved in a clinical study; the principal investigator is the primary researcher that shares more of the responsibility of conducting the trial.

Phase – the phase of the trial gives us information explicitly or implicitly about the extent to which an intervention has been explored and assessed and what can be expected of it; for example, a drug in phase I is further from being proven safe and effective than a drug in phase III, whereas a drug in phase IV (also called ‘post-market’ phase) has already been introduced in the general population but some fine-tuning is still needed.  

Placebo – also known as a ‘sugar pill’, the placebo is an inactive substance given to one arm of the trial in order for the investigational drug to be compared against it.

Primary purpose – the primary purpose of a study is the main reason for the research to be conducted in the first place; there are 9 main purposes for clinical studies according to the initial interest of the researchers, their main hypothesis, aim, scientific field and so on.

Protocol – a thorough description of the clinical trial; the protocol typically explains in detail the trial objectives and methods and it includes information about everything the participant must know in order to give their informed consent – all the interventions and tests that will take place, how and when participants will be monitored – everything is in the protocol.

Randomization – randomization refers to the way participants are allocated to different arms of the trial; randomized allocation is done in order to avoid skewing the data and to guarantee the scientific integrity of the study, and it’s considered the better practice of allocating participants.  

Sponsor – a sponsor is an organization, pharmaceutical company, a charity, an institute or any other entity that funds the clinical trial; clinical trials can also be funded by the government.

SAP, Statistical analysis plan – the written description of the methods that are going to be used in analyzing the data collected from the trial.

Study design – this a whole field of research in and of itself, there are researchers dedicated to determining the most effective ways to ‘design’ a study; what study design simply means is the sum of investigative methods and strategies used to construct a study.

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