Adverse Reaction
"Any harmful and undesired response to a medicinal product which occurs with doses normally used for prophylaxis, diagnosis or treatment or for modification of physiological functions and where there is a suspicion of causal relation between the adverse occurrence and the use of the medicinal product."

In the notification of an adverse reaction it is also important to distinguish two concepts that easily lead to confusion: severity/intensity and seriousness.

The intensity or severity is based on the intensity of the adverse reaction, being classified into mild, moderate and severe.

The seriousness is related with the evolution/outcome of the adverse reaction, being defined by the criteria described for a severe adverse reaction.

Serious Adverse Reaction
Any adverse reaction which results in death, that is life-threatening, that requires or prolongs hospitalisation, that results in a persistent or significant incapacity, or that involves a congenital abnormality. The health care professional may consider if it is a severe adverse reaction despite it does not obey to any of the criteria mentioned above (medically important).