What are the two types of pharmacovigilance? A Deep Dive into Active and Passive Surveillance

October 8, 2025 •

4 min read

Adverse drug reactions (ADRs) are a major public health concern, with some estimates suggesting they are the 4th leading cause of death in the U.S., ahead of diabetes and accidents [1.4.1]. To protect public health, regulatory bodies and pharmaceutical companies use two primary methods to monitor drug safety. So, what are the two types of pharmacovigilance? They are active and passive surveillance [1.2.2].

Quick Summary

Pharmacovigilance is the science of monitoring the effects of medical drugs. Its two main approaches are passive surveillance, which relies on voluntary reports, and active surveillance, which uses proactive methods to collect safety data [1.2.1, 1.2.2].

Key Points

Two Main Types: The two types of pharmacovigilance are passive and active surveillance [1.2.2].
Passive Surveillance: Relies on the voluntary, spontaneous reporting of adverse drug reactions (ADRs) by healthcare professionals and patients [1.5.5].
Active Surveillance: Involves proactive, systematic efforts to collect drug safety data through methods like registries and database studies [1.2.1].
Core Difference: Passive surveillance is reactive and cost-effective, while active surveillance is proactive, more resource-intensive, but yields more reliable data [1.2.2, 1.3.3].
Major Challenge: The biggest limitation of passive surveillance is significant underreporting of adverse events [1.3.3].
Calculating Risk: Active surveillance allows for the calculation of incidence rates for ADRs, which is not possible with passive systems due to an unknown denominator [1.3.2].
Complementary Roles: Both systems are crucial and work together to form a comprehensive drug safety monitoring program [1.2.2].

The Foundation of Drug Safety: Understanding Pharmacovigilance

Pharmacovigilance is the science and set of activities related to the detection, assessment, understanding, and prevention of adverse effects or any other drug-related problems [1.2.4]. Even after rigorous pre-market clinical trials, a drug's full safety profile is not completely known [1.5.6]. Clinical trials often involve a limited number of people under controlled conditions, excluding vulnerable populations like the elderly or those with multiple health issues [1.5.6]. Post-marketing surveillance becomes crucial to monitor a drug's performance in a real-world setting, where millions of diverse individuals use it. This ongoing monitoring helps ensure that a drug's benefits continue to outweigh its risks. The core of this post-marketing effort is driven by two distinct but complementary approaches: passive and active pharmacovigilance [1.2.2].

Passive Pharmacovigilance: The Cornerstone of Signal Detection

Passive surveillance is the most common form of pharmacovigilance globally, largely due to its cost-effectiveness and broad reach [1.2.2]. It is a reactive method that depends on the voluntary submission of suspected adverse drug reaction (ADR) reports from healthcare professionals, patients, consumers, and pharmaceutical companies [1.5.7, 1.3.4].

Methods and Examples: The primary method is spontaneous reporting systems (SRS). Healthcare providers or patients who suspect an ADR can submit a report to a national regulatory authority [1.5.5].

FDA's MedWatch and Adverse Event Reporting System (FAERS): In the United States, healthcare professionals and consumers can report adverse events through the MedWatch program, which feeds into the FAERS database [1.2.2, 1.6.2].
WHO's VigiBase: This is the World Health Organization's global database of individual case safety reports, collecting data from over 130 countries [1.4.3].
Yellow Card Scheme (UK): A well-known system in the United Kingdom for collecting suspected ADRs [1.5.6].

Advantages:

Wide Coverage: It can identify rare, unexpected, or long-term ADRs that were not apparent in clinical trials [1.2.2].
Cost-Effective: It is less resource-intensive than active surveillance because it doesn't involve actively seeking out data [1.2.2].
Early Signal Generation: It serves as an essential tool for generating early warnings or "signals" about potential drug safety issues [1.5.1].

Disadvantages:

Underreporting: This is the most significant challenge. Many ADRs go unreported due to lack of awareness, time constraints, or uncertainty about the cause [1.3.3].
Data Quality: The quality and completeness of reports can vary widely, making robust analysis difficult [1.3.3].
Inability to Calculate Incidence: Since the total number of people exposed to the drug is unknown (the denominator), it is difficult to calculate how frequently an ADR occurs [1.3.2, 1.5.6].

Active Pharmacovigilance: A Proactive Search for Safety Data

Active surveillance takes a proactive approach to collecting drug safety data. Instead of waiting for reports, this method involves structured and pre-planned efforts to systematically gather information about drug effects in a specific population [1.2.1, 1.2.2]. It is more resource-intensive but generally yields more reliable and complete data [1.2.2, 1.3.3].

Methods and Examples: Active surveillance uses various pharmacoepidemiological study designs.

Cohort Event Monitoring (CEM): A specific group of patients (a cohort) prescribed a particular drug is monitored over time to identify any adverse events [1.2.2].
Registry-Based Studies: Patient registries, which collect data on individuals with specific diseases or exposures, can be used to evaluate the long-term safety of certain treatments [1.2.2].
Prescription Event Monitoring (PEM): This method tracks prescriptions and then follows up with the prescribing doctor or patient to inquire about any events that occurred since the drug was started [1.2.2].
Database Analysis: Proactively analyzing large electronic health records (EHR) or health insurance claims databases to look for associations between drugs and health outcomes [1.2.1]. The FDA's Sentinel System is a prime example, using data from various healthcare organizations to monitor drug safety [1.6.2].

Advantages:

More Accurate Data: Provides more controlled and systematic data, leading to a clearer safety profile [1.2.1].
Can Calculate Incidence: Because it defines a specific population under study, active surveillance can determine the incidence (rate of new cases) of an ADR [1.3.2].
Reduced Reporting Bias: It is less susceptible to the biases inherent in voluntary reporting [1.3.3].

Disadvantages:

Resource-Intensive: Requires significant funding, time, infrastructure, and trained personnel [1.3.3].
Complex Implementation: Setting up active surveillance systems can be complex and challenging [1.2.2].
Limited Scope: It typically focuses on specific drugs or safety concerns, rather than providing the broad-ranging view of passive systems.

Comparison Table: Active vs. Passive Pharmacovigilance


Feature	Passive Pharmacovigilance	Active Pharmacovigilance
Approach	Reactive (waits for reports) [1.5.5]	Proactive (actively seeks data) [1.2.1]
Data Source	Voluntary spontaneous reports from HCPs and patients [1.2.2]	Pre-defined processes like cohort studies, registries, EHR analysis [1.2.2, 1.6.6]
Cost	Lower, less resource-intensive [1.2.2]	Higher, requires significant investment [1.3.3]
Key Strength	Broad signal detection, identifies rare ADRs [1.2.2]	Stronger evidence, can calculate risk/incidence rates [1.3.2]
Key Weakness	Significant underreporting and data quality issues [1.3.3]	Complex, expensive, and often has a narrower focus [1.2.2]
Example Systems	FDA's FAERS, WHO's VigiBase [1.2.2, 1.6.2]	FDA's Sentinel System, specific patient registries [1.6.2, 1.6.6]

The Future of Pharmacovigilance

The field of pharmacovigilance is constantly evolving. The increasing volume of health data from sources like electronic health records, patient forums, and wearable technology presents both challenges and opportunities [1.7.4]. The future lies in leveraging technology like artificial intelligence (AI) and machine learning to analyze these vast datasets more efficiently, improving the speed and accuracy of signal detection [1.7.6]. Furthermore, there is a push towards greater patient involvement, empowering patients to contribute directly to safety monitoring [1.7.5]. Combining the strengths of both active and passive systems, enhanced by new technologies, will create a more robust and proactive global drug safety net [1.2.2, 1.7.5].

Conclusion

Both passive and active pharmacovigilance are indispensable tools for monitoring medication safety post-approval. Passive surveillance acts as a wide net, capturing a broad range of potential safety signals at a low cost, while active surveillance provides a more focused and rigorous method for confirming signals and quantifying risk [1.2.2]. They are not mutually exclusive; a strong pharmacovigilance strategy integrates both approaches to create a comprehensive system that protects public health by ensuring the medicines we rely on are acceptably safe.

For more information on the FDA's active surveillance systems, you can visit the FDA Sentinel Initiative page. [1.6.2]

Frequently Asked Questions

The primary goal is to detect, assess, understand, and prevent adverse effects or any other drug-related problems to ensure the safety of medicines [1.2.4].

Spontaneous reporting is the core method of passive surveillance, where healthcare professionals and patients voluntarily submit reports of suspected adverse drug reactions to regulatory authorities [1.5.1].

The FDA's Sentinel System is an active surveillance system. It proactively uses electronic healthcare data from a large network to monitor the safety of medical products [1.6.2].

Underreporting is a major problem because it can delay the identification of potential safety issues, leading to an incomplete understanding of a drug's true risk profile [1.3.3].

Yes. If pharmacovigilance activities reveal that a drug's risks outweigh its benefits, regulatory authorities can take action, which may include changing the product label, restricting its use, or withdrawing it from the market [1.5.6].

An Adverse Drug Reaction (ADR) is a harmful and unintended response to a drug that occurs at doses normally used for prophylaxis, diagnosis, or therapy [1.2.5].

Healthcare professionals (doctors, pharmacists, nurses) and patients/consumers are all encouraged to report suspected ADRs to help monitor drug safety [1.5.4, 1.5.7].