Adverse reactions are unwanted and negative reactions between a person and a drug. They can be dose-dependent and predictable or idiosyncratic and unpredictable. Severity varies and is monitored by organizations like the FDA and WHO.
An adverse reaction — also sometimes called an adverse drug reaction, adverse drug event, adverse event, or adverse effect — is a reaction between a person and a drug or other type of drug that is usually unwanted and bad. Unlike a side effect which may be unintended but potentially positive, an adverse reaction is almost always negative and can have different causes and levels of severity. In many areas, government agencies require extensive testing of a new drug or pharmaceutical product to ensure product safety and attempt to discover any adverse effects before a product is made widely available to the public.
There are several main categories that an adverse reaction can fall into, including dose-dependent and predictable reactions, unpredictable or idiosyncratic reactions, and allergic reactions. Dose-dependent reactions are typically predictable, and these types of reactions can usually be recreated in an experimental or laboratory setting with reliable results. As research and understanding of pharmacology has improved over the years, these types of reactions have become more common as fewer reactions remain unexplained. Understanding these types of reactions is especially important as it can ensure fewer incidental adverse drug reactions occur.
Idiosyncratic reactions, however, are not dose-dependent and are typically unpredictable. This type of adverse reaction may not be easily replicated in experiments or studies. These are often allergic reactions in which the particular process by which an organism reacts negatively to the drug is not fully understood or in which it is not possible to establish a clear commonality between subjects with this adverse reaction. Idiosyncratic reactions can be the most problematic for a pharmaceutical company as they can be the most difficult to fully understand and can lead to unintended or fatal illness.
The level of severity of an adverse reaction can vary greatly and depends on the drug and how it interacts with the body. Different scales are used by different organizations, with different language and specifications for each level of severity. Typically, the word “severe” is used to describe a potentially fatal or life-threatening reaction that can lead to hospitalization or disability, although sometimes “lethal” is used instead. “Severe” is often used as a modified term to denote a sliding scale such as “low severity” or “high severity” depending on how unpleasant or painful a reaction might be.
In the United States, the Food and Drug Administration typically oversees the release of drugs and medications to ensure the safety of those products. The European Medicines Agency represents the European Union in investigating any potential reactions involving medicines. On a global scale, the World Health Organization monitors various pharmaceutical products for potential adverse effects.
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