What is meant by idiosyncrasy in relation to medication?

Idiosyncrasy in relation to medication refers to an unexpected reaction to a drug that typically does not happen in most individuals. This type of response is usually not predictable based on the known pharmacological effects of the medication or its common side effects. Idiosyncratic reactions are often unique to an individual and can vary widely among patients. They can be influenced by genetic factors, underlying health conditions, or other individual characteristics that affect how a person metabolizes or reacts to a drug.

In contrast, the expected response to medication is predictable based on clinical studies and knowledge of the drug's pharmacodynamics. Common side effects are well-documented reactions that many patients might experience, and allergic reactions specifically involve a hypersensitivity response, which is also a recognized and expected category of adverse drug reactions.