Clinical Trial Glossary

Clinical Studies & Trials

Clinical Trial Glossary

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Cross-over: Participants get both the placebo and experimental treatment but do not know the order.


Discovery: Very early research conducted to help better understand the disease, identify new drug candidates, optimize drug compounds, and/or understand the mechanism of action for a drug.

Double-blind Study: Study where neither the patient or the investigator know if they are receiving the active medication or the placebo.


Investigational Medicinal Product Dossier (IMPD): Regulatory filing in Europe to begin clinical testing in humans.

Investigational New Drug (IND) Application: Regulatory filing in the United States to begin clinical testing in humans.


Marketing Authorization Application (MAA)/New Drug Application (NDA): MAA is the regulatory filing to support a drug’s approval in the European Union (EU); NDA is the regulatory filing in the United States.


Natural History Studies: Type of observational study designed to look at the course of a disease without any type of treatment or intervention (other than the standard of care). Natural history studies help researchers better understand the course of the disease over time and what demographic, genetic or environmental factors are associated with the disease progression.


Phase 1: Studies in humans that assess the safety and toxicity of a treatment in a small group of healthy volunteers or patients with the disease of interest.

Phase 2: Studies that further test the safety and begin to test the effectiveness of the drug, often at a variety of doses.

Phase 3: Studies that assess the safety and effectiveness of the drug in a larger group of patients. The drug is typically compared to standard treatment(s) or to no treatment (e.g. natural history study or a placebo).

Phase 4: Studies designed to further understand a drug’s safety and/or effectiveness after regulatory approval. 

Placebo (control): An inactive product that resembles the test medicine or procedure, but without a treatment value. A placebo can be a pill, a powder, or a solution that resembles the test drug, but has no physical effect.

Pre-Clinical: In-vivo studies conducted under good laboratory practices to assess toxicity and dosing for human trials.

Primary Endpoint: The primary (or most important) question being asked by a trial sponsor.


Randomization: The process of being assigned to a treatment group (e.g. placebo or active drug) within a clinical trial. Randomization is done to help demonstrate a new medicine’s therapeutic effectiveness.


Safety Profile: An outline of the risks and potential negative side effects of a treatment that is weighed against the possible benefits and used to determine if a treatment will be made available.

Study Blinding: Study where the patients do not know if they are receiving the active drug or a placebo. Blinding is done to prevent bias and influencing the trial results.

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