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By reporting suspected side effects, patients and healthcare professionals provide important information about medicines.
Patients are encouraged to report any side effects that occur after using a medicine, even if they are unsure whether the medicine caused them.
Medicines are tested extensively in clinical trials before they are authorised. However, their side effects cannot be entirely understood before they are used by many people over a long period of time.
Regulators analyse reports that patients and healthcare professionals submit, alongside information from a range of other sources. This helps them identify possible new safety concerns and ensure medicines are used as safely as possible.
For more information, see:
Anyone can report a suspected side effect on a medicine as long as they have the necessary details. They could be the patient, the patient’s carer, a doctor, nurse or pharmacist.
Patients can report a suspected side effect themselves or ask their healthcare professional to report it for them.
Each EU country has a tool for reporting suspected side effects. Information on how to report is available on:
This includes the brand name and the active substance
Batch number can be found on the medicine's packaging
This includes the person's age and sex
If so, did the side effect stop?
Other medcines can include non-prescription, herbal or birth control medicines
Once someone reports a suspected side effect, the national competent authority reviews the report to check that it contains enough information to assess it. This includes details such as:
If information is missing, the national competent authority may contact the person who submitted the report to ask for more details.
The national authority records the report in its database and classifies it according to severity and impact on health. It then sends the report to the EudraVigilance, the EU database of suspected side effects. EudraVigilance is one of the largest pharmacovigilance databases in the world. It contains tens of millions of reports.
EMA manages the reports submitted to the EU database by national competent authorities and pharmaceutical companies. It checks the quality of the information and removes duplicate reports so that the data can be analysed.
EMA continuously screens the data to detect unusual or unexpected patterns. If a potential safety issue is identified for a medicine, regulators assess it together with other available information about the medicine.
If there is at least a reasonable possibility that a medicine could have caused a suspected side effect, this information is added to the medicine’s product information.
As millions of reports are collected and screened in the EU every year, it is not possible to provide individual feedback to everyone who reports a suspected side effect. Patients and healthcare professionals can check the package leaflet and summary of product characteristics (SmPC) for up-to-date information.
For more information, see:
It is important to understand that just because someone experiences an unwanted effect after taking a medicine, it does not necessarily mean the medicine caused it.
This is a key difference between correlation (two things happening at the same time) and causation (one thing actually causing the other).
For example, a new medicine is approved to treat high blood pressure and becomes widely used in clinical practice. Some patients report that they are experiencing headaches. However, headaches are also common in people with high blood pressure, regardless of treatment.
Regulators will carefully assess reports of this suspected side effect in EudraVigilance, evaluating important questions that help them to conclude on causation, such as:
Additionally, medicines regulators will also determine if there are any confounders. These are other factors that can be responsible for the suspected side effect other than the medicine itself.
A possible confounder in the case of headaches could relate to poor compliance, which means that the patient was not taking their blood pressure medicine every day. The headaches could therefore be due to untreated high blood pressure rather than the medicine itself.
Furthermore, if higher doses of the medicine lead to more frequent or worse headaches, it supports the idea that the medicine is causing them.
This explains why a single report of a suspected side effect is not enough to confirm that a medicine caused it. More evidence is needed, such as:
Medicines regulators carry out detailed assessments of all available data to draw robust conclusions.
Medicines regulators use specialised statistical methods to monitor the data in EudraVigilance.
One important approach involves looking for patterns in reported side effects. Specifically, whether a suspected side effect is reported more often with a particular medicine than would normally be expected.
These patterns are known as signals of disproportionality. They can be linked to potential safety signals, although further evaluation is always needed to confirm whether the medicine is actually causing the effect.
To detect such signals, regulators will compare how often a side effect is reported for one medicine with how often it is reported for other medicines. This is a statistical measure called the reporting odds ratio (ROR). If the ROR is higher than expected, it may point to a possible safety concern that needs closer examination.
During the COVID-19 pandemic, regulators complemented these methods with another type of analysis which compares the number of reported cases of a suspected side effect for a given vaccine to the number expected in the general population based on background rates. This is called observed versus expected (O/E) analysis.
This approach was particularly useful for evaluating suspected side effects following the mass vaccination campaign, given the large volume of data and the need for rapid assessments. To be able to carry out such analyses, even before the vaccination campaigns started, EMA worked very closely with researchers to determine the expected frequency for a wide range of effects in the general population.
Detailed information on how suspected side effects reported during the COVID-19 pandemic were analysed is available in a pharmacovigilance report published on the EMA website.
For more information, see:
Anyone can access information on suspected side effects that patients and healthcare professionals reported across the EU. This is possible for each medicine or active substance in the European suspected adverse drug reactions database.
These data come from the EudraVigilance database. Users can analyse them by country, age group and type of side effect reported.
These reports do not necessarily reflect a real safety issue with a medicine. Many of the events reported may have been caused by another illness or be associated with another medicine that a patient takes at the same time. Only a careful assessment can determine if the medicine caused the problem.
During the COVID-19 pandemic, a lot of incorrect figures about reports of suspected side effects and deaths following COVID-19 vaccination circulated on social media and various websites. Some of these figures came from misunderstanding the data in the European database of suspected side effects.
It is not possible to use the data from this website to calculate the total number of fatal cases reported for a given medicine or the total number of a specific reaction (such as myocardial infarction). This is because one individual case may contain more than one suspected side effect. Consequently, the sum of the number of suspected side effects will always be higher than the total number of cases.
EudraVigilance, the EU database of suspected side effects, protects personal data using a method called pseudonymisation. This means it replaces details that could identify someone (like their name or patient ID) with codes.
This way, regulators can study medicine safety data without seeing who the person is, in line with EU privacy rules.
An update log is available to show the date and summary of changes to this webpage. It does not include updates to linked documents or minor edits like typos or broken link fixes.
The tracking of updates begins in October 2026.
30 October 2026
Page first published