The World Health Organization (WHO) defines it as:
“A response that is harmful or unintentional and that occurs with doses normally used in man.”
According to the above definition, an adverse reaction is any clinical manifestation (sign, symptom or laboratory disorder) that occurs in a patient and has a cause-and-effect relationship with the drug. It is also called a side effect or side effect.
We speak of a suspected adverse reaction when, despite not being certain that there is a cause-effect relationship between the drug and the clinical manifestation, there is some indication or appearance that such a relationship exists.
The term suspected adverse reaction is distinguished from the adverse event when there is no cause-effect relationship between the drug and the clinical manifestation, or it is not known whether there is a cause-effect relationship.