What type of effect is caused by a hypersensitive reaction to a substance perceived as foreign?

Allergic effects occur when the immune system reacts to a substance that is typically harmless but is perceived as foreign, leading to hypersensitivity. This can involve a range of symptoms from mild reactions, such as itching and rashes, to severe reactions like anaphylaxis. The response is mediated by the release of histamines and other chemicals from immune cells, particularly upon subsequent exposures to the allergen.

In this context, allergic effects are specifically tied to the immune system's exaggerated response. Other potential reactions mentioned, such as side effects, toxic reactions, and adverse reactions, refer to different phenomena. Side effects are generally unintended effects that occur in addition to the desired therapeutic effect of a drug. Toxic reactions involve harmful effects resulting from excessive doses or prolonged exposure to a substance, while adverse reactions can encompass a broad range of harmful effects that may occur with a medication, not necessarily linked to an allergic response. Thus, the identification of allergic effects as the correct choice underscores the distinctive nature of hypersensitivity reactions in pharmacology.