In a clinical trial or research study, a secondary endpoint refers to an outcome measure that is of lesser importance or serves as a supplementary measure compared to the primary endpoint. While the primary endpoint is the main outcome measure used to evaluate the effectiveness or efficacy of an intervention, secondary endpoints provide additional information or explore other aspects of the treatment's effects.

Secondary endpoints are often included to gather more comprehensive data on the intervention being studied. They can include various clinical, laboratory, or patient-reported measures that provide insights into secondary or exploratory outcomes. Examples of secondary endpoints may include:

Secondary clinical outcomes: These are additional clinical measures that assess different aspects of the disease or condition being studied. For example, in a clinical trial evaluating a new drug for hypertension, the primary endpoint may be a reduction in systolic blood pressure, while secondary endpoints could include measures like diastolic blood pressure, heart rate, or changes in lipid profiles.

Safety or adverse events: While the primary focus of a trial is often on efficacy, it is crucial to evaluate the safety profile of the intervention. Secondary endpoints related to safety may include the incidence of adverse events, drug toxicity, or other treatment-related complications.

Quality of life or patient-reported outcomes: Some studies include secondary endpoints that assess the impact of the intervention on patients' quality of life, symptoms, functional status, or other patient-reported outcomes. These measures provide insights into the treatment's effect on the patients' overall well-being and subjective experiences.

Exploratory biomarkers or surrogate endpoints: Secondary endpoints can also involve the assessment of biomarkers or surrogate endpoints that are not the primary focus of the study but provide additional information about the intervention's mechanism of action or its effect on underlying biological processes.

Secondary endpoints are typically pre-specified in the study protocol, and their analysis is performed after the primary endpoint analysis. It's important to note that secondary endpoints are considered exploratory and should be interpreted with caution, as they are more susceptible to chance findings or biases. However, they can still provide valuable information for further investigation, hypothesis generation, or supporting the overall understanding of the intervention's effects