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At Pfizer, our commitment to medicine safety begins in the research laboratory and continues for as long as the medicine is prescribed to patients anywhere in the world.

Receiving regulatory approval for a medicine is a significant judgement on the safety of a medicine, but it is not the final safety checkpoint. Pre-registration clinical trials cannot detect every possible side effect, and more may become apparent because the drug is used:

  • in much larger number groups of patients
  • for longer periods of time – sometimes for months or years 
  • in a more diverse patient population
  • under ‘real-world’ circumstances rather than the more predictable and closely monitored conditions of clinical trials

It is very important that we monitor how our medicines act in real-world patients, who are not as closely monitored and supervised as participants in clinical studies. In the real world, patients:

  • don’t always take their medication as recommended 
  • don’t always adhere to dosing recommendations
  • may have underlying conditions that may affect the expected performance of a medicine 
  • may take other medication, including non-prescription medication

In addition to these factors, healthcare professionals may prescribe a drug for conditions other than those approved by the regulatory agency, or for shorter or longer periods of time than those recommended. Patient follow-up may for all sorts of reasons be less comprehensive. These different conditions provide the opportunity to build up knowledge and may go beyond what was known about the safety characteristics of the medicine at the time of approval.

We encourage healthcare professionals to report any ‘adverse events’ (side effects) in their patients on a Pfizer medicine, whether it is thought the event was caused by our medicine or not. We also encourage reporting if the medicine fails to work as expected. All Pfizer employees are fully trained in how to recognise and report an adverse event. We have to report all such events to the regulatory bodies, whether or not we can confirm their accuracy.

If you are taking or prescribing a medicine and experience any side effects, which are not listed on the patient information leaflet, you should immediately report these to your doctor, to another healthcare professional (such as a nurse or carer) or to the company which produced your medicine. The telephone number for the Drug Safety Group at Pfizer is 01304 616161.

The MHRA can be contacted through its Yellow Card reporting system at

It is extremely rare for information to be discovered after a drug has been approved which will lead to a medicine being withdrawn or its use being severely restricted. However, when this occurs, it usually receives considerable public attention.

The more common scenario is that newly identified safety issues help the pharmaceutical companies, working with regulatory agencies, to better understand who should or should not take the medicine, or how to update dosing recommendations.