Commonly Used Terms in Clinical Trials

• Open Label Study: Informing all parties of the study (sponsor, investigator, and volunteer) regarding the drug and the dose administered (non-blinded study).
• Adverse Effect: These are harmful and unintended effects that occur in volunteers during the use of a human medicinal product at normal doses accepted for the purpose of prevention from disease, diagnosis or treatment of a disease, or improvement, correction, or modification of a physiological function, or during the use of the investigational medical device.
• Antigen: A substance of protein structure, such as a virus, bacterium, or parasite, that leads to the formation of antibodies when it enters the body.
• Antibody: A substance produced by the organism to render antigens entering the body harmless.
• Bioequivalence: The degree of similarity between two pharmaceutical equivalent preparations, following their administration at the same molar dose, such that their bioavailability and thus their effects are essentially the same in terms of both efficacy and safety.
• Bioavailability: The rate and extent to which the active substance and its therapeutic moiety are absorbed from the pharmaceutical form and enter the systemic circulation, thereby being present at the site of action in the body or in biological fluids reflecting it, generally serum or plasma.
• Double Blind: A situation in which neither the volunteers nor the investigators involved in a clinical trial know which treatment the volunteers are receiving.
• Double Dummy: A blinding method used to mask which products are administered to research groups in blinded studies where an investigational product is to be compared with another product and it is not possible to ensure that both groups of products have a similar appearance. Accordingly, for example, masking is applied to the research groups by administering a placebo tablet and an ampoule containing the active substance to one group, and a tablet containing the active substance and a placebo ampoule to the other group.
• Multicentre Clinical Trials: A clinical trial conducted in more than one centre according to a single protocol, which therefore has one coordinator but more than one principal investigator.
• Sponsor: Refers to the person, institution, or organization responsible for the initiation, management, or financing of a clinical trial.
• Dose: The amount of medicine or vaccine given to a person at one time.
• Efficacy: The adequacy of the product in providing beneficial effects during the disease process. In a controlled clinical trial; it is the percentage reduction in the incidence of disease observed in vaccinated individuals compared to unvaccinated individuals in the presence of equal exposure.
• Effectiveness: The drug showing its intended effect on a disease state defined by adequate and controlled research. Under real-life conditions; it shows how much specified risks such as disease, hospitalization, and death are reduced in vaccinated individuals compared to those who are not vaccinated; it is affected by the characteristics of the vaccinated individuals and program-related factors such as real-life application conditions; cold chain, vaccine preparation, and application technique.
• Effective Dose: The dose of the investigational product that provides the "effectiveness" result as defined in the study protocol.
• Phase Studies: These are the clinical research periods that must be completed during the development of a new drug or vaccine. All research conducted before the investigational product is tested in humans is called “pre-clinical studies.”
• Phase 0 Studies: These are studies conducted on a very small number of volunteers before Phase I studies in order to design new candidate therapeutic agents.
• Phase I Studies: Also referred to as first-period studies. This is the clinical research period in which investigational products are tested by being administered to a sufficient number of healthy volunteers selected according to the nature and character of the research, or to patient volunteers in cases where studying in healthy volunteers is not appropriate, in order to determine the pharmacokinetic properties, toxicity, and effect on body functions of the products.
• Phase II Studies: Also referred to as second-period studies. This is the clinical research period in which the investigational product is tested by being administered to a sufficient number of volunteer patients selected according to the nature and character of the research, for the purpose of investigating the therapeutic dose limits, clinical efficacy, and safety of the product.
• Phase III Studies: Also referred to as third-period studies. This is the clinical research period in which the investigational product, having passed through Phase I and Phase II periods, is tested by being administered to a sufficient number of volunteer patients selected according to the nature and character of the research, in terms of its effectiveness, safety, investigation of a new indication, different doses, new routes and methods of administration, a new patient population, and new pharmaceutical forms.
• Phase IIIa Studies: These are studies conducted after the efficacy of the drug or vaccine has been demonstrated and before the application for marketing authorization.
• Phase IIIb Studies: These are studies conducted after the application for marketing authorization of the drug or vaccine has been submitted to the health authority, but before the marketing authorization approval is obtained.
• Phase IV Studies: Also referred to as fourth-period studies. All research conducted regarding the approved indications, posology, and administration methods of drug or vaccine products that have received marketing authorization in Türkiye after they have been placed on the market, and all studies aimed at further examining the effectiveness and safety of drugs and vaccines, are called phase IV studies.
• Pharmacovigilance: Scientific studies related to the detection, assessment, identification, and prevention of adverse effects and other potential problems related to drugs or vaccines.
• Subject/Volunteer: Patients or healthy individuals who participate in a clinical trial by obtaining their own written consent or the written consent of their legal representative.
• Cell Culture: The process of growing cells under controlled conditions.
• Immunogenicity: The ability of a foreign substance, such as an antigen, to trigger an immune response in the body of a human or another animal.  
• Good Clinical Practices (GCP): These are the rules that cover regulations on subjects such as the design, conduct, monitoring, budgeting, evaluation, and reporting of research, the protection of all rights and the physical integrity of the volunteer, ensuring the reliability of research data, and maintaining confidentiality, in order to ensure that research is conducted in accordance with international scientific and ethical standards, and which must be followed by the parties participating in the research.
• Good Laboratory Practices (GLP): These are the principles that determine the practices and conditions necessary for the planning, implementation, monitoring, documentation, clarification, reporting, and archiving of laboratory studies.
• Good Manufacturing Practices (GMP): Standards that must be applied in the production of drugs, vaccines, and biological substances for humans and animals.
• In-House Blinding: A situation where the administration of the study product is performed by a staff member who has no knowledge of the study, generally in cases where it might be discernible which drug or vaccine is which during the administration of the investigational product.
• Clinical Trial: According to the GCP guideline, a clinical trial refers to studies conducted on humans for the purpose of uncovering or verifying the clinical, pharmacological, or other pharmacodynamic effects of one or more investigational products; identifying adverse events or reactions; determining their absorption, distribution, metabolism, and excretion; and investigating their safety and efficacy. Furthermore, in its broader scope, a clinical trial refers to prospective studies conducted to compare the effect and value of an intervention applied in any clinical situation with a control group. The terms “clinical study” and “trial” are also used in the same sense. A clinical trial does not only cover research conducted with drugs or vaccines; this term also encompasses studies conducted with surgical and similar invasive interventions, medical devices and prostheses, diets, physical therapy, and diagnostic tools.
• Cohort: A group of individuals under follow-up who are determined to have one or more similar characteristics at the beginning.
• Control Group: The comparison group that is not treated with the investigational drug or vaccine. No treatment, a different treatment, or a placebo can be examples for this group.
• Controlled Study: A study in which the investigational product is compared with a treatment that has a known effect.
• Blinding: It refers to the fact that during the research, the identity of the investigational product administered to the volunteer is not known by one or more parties involved in the research, such as the investigator, volunteer, or monitor. Single blinding generally refers to the volunteer not being informed, while double blinding generally refers to the volunteer, investigator, monitor, and in some cases, the data analysts not being informed about the treatment provided.
• Conditional Marketing Authorization (Accelerated Approval): It is a mechanism used by TİTCK (Turkish Medicines and Medical Devices Agency) during processes where efficacy and safety data are positive at an early stage and close follow-up continues, aimed at the rapid clinical introduction of drugs or vaccines that have the potential to provide significant benefits in the treatment or prevention of serious or life-threatening diseases such as outbreaks and pandemics.
• Methodological Research: A type of research that includes mathematical modelling methods that can be applied to various subjects, in addition to research conducted to investigate how accurate, reliable, and valid newly developed diagnostic methods are.
• Primary Vaccination: The first vaccination performed against a specific pathogen.
• Placebo: An inactive substance or procedure designed similarly to the potential treatment.
• Placebo Effect: These are the effects that occur after a person takes the placebo. People are generally affected by the placebo in the direction of what kind of effect they expect from the drug, vaccine, or device.
• Placebo-Controlled Trial: A comparative study that compares the new product related to the research with a placebo.
• Prevalence: The proportion of individuals in a specific population, within a specific period of time, who have a specific disease or diseases included within the scope of the study.
• Prospective Study: Studies in which volunteers/patients are included forward-looking according to the criteria defined in the protocol.
• Randomization: The process of assigning volunteers to treatment or control groups by chance in order to reduce bias.
• Booster Vaccination: A reinforcement vaccine administered to extend the duration of the vaccine's effect.
• Retrospective Study: Studies in which retrospective data are collected.
• Single-Arm Trials: Studies in which there is only one group and all volunteers in this group are treated in the same way.
• Single Blinding: A type of blinding in which the patient/volunteer does not know what they are receiving.
• Bias: A systematic error made at any stage of the research that affects the results.