Adverse drug reaction

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An adverse drug reaction (abbreviated ADR) is a term to describe the unwanted, negative consequences sometimes associated with the use of medications. ADR is a particular type of adverse effect. The term is preferred over the colloquial and imprecise "side effect", as the term "side effect" implies the potential for beneficial consequences and that the effects are not explained by the pharmacological actions of the drug. The focused study of ADRs is the concern of the field known as pharmacovigilance

While ADR is probably the most precise term to describe the concept, it is not widely used in the community since it may be perceived as jargon and because of the negative-associations with the term "drug". Alternative terms with equivalent meaning to ADR include: side effect, adverse event, adverse effect, etc.

There are many types of ADRs:

Type A, pharmacologically predictable
Type B, bizarre and unpredictable
Type C, arising from chronic use
Type D, delayed reaction
Type E, end of dose reaction
Type F, Failure of therapy

[edit] Why do Adverse Drug Reactions (ADRs) matter and how do they happen?

ADRs matter because pharmaceutical products and other substances taken for medical purposes have the potential for harming patients, even killing them. ADRs happen for many reasons, some inevitable and unavoidable, some preventable.

The inevitable reasons are:

The effects of any medical intervention cannot be predicted with absolute certainty
There is no drug or medical intervention which will not have some negative and undesirable effect on someone, somewhere at some time
Information about rare events may, by their very nature, not be available until they happen.

The preventable reasons include:

An error in diagnosing the disease
Prescription of the wrong drug for the disease
Prescription of the wrong dose of the right drug
Choice of the right drug for the disease, but maybe the wrong drug for the patient, because of some genetic or ethnic predisposition, age, some other illness or medication, some allergy or intolerance
Choice of an appropriate drug but without taking into account potentially harmful interactive effects with other drugs or substances being taken
In relation to all the above, the full indications, contraindications and risks of the drug may not have been read or fully understood
The patient may not comply with the doctor’s advice or manufacturer’s advice in the patient information leaflet
People choosing drugs and other substances for their own medication may cause problems.

The remedies for these hugely challenging problems:'

A higher priority in medical training in taking case-histories, diagnostic skills, pharmacology, and the recognition and reporting of adverse effects
Greater awareness by healthcare professionals and the public about the complexities and benefit-harm-risk profiles of medical interventions
More effective communication and openness about the nature of drugs and their effects and the degree of uncertainty associated with them
Public education and debate about the benefits, harm and risks of medical interventions and agreement about the balance of benefit, harm and risk which is acceptable, given that there will always be some uncertainty.
Wider discussion and education in the nature of risk in general and its communication, and in the individual variables affecting perception and acceptance of risk.