Drugs may be absorbed by mouth, by injection, by inhalation, or by contact. They may be well accepted, or they may cause intolerance or allergy. Intolerance is an exaggerated response to a large quantity of a drug, while allergy is sensitivity to the drug regardless of the quantity used.

Allergy to a drug assumes one of [...]

Occasionally people develop psychogenic reactions to food when there is no physical response. This can happen if someone becomes convinced that they are food-allergic or food-intolerant without undergoing proper diagnosis. They may decide that they react to particular foods, on the basis of a bogus diagnostic test or an elimination diet that is not properly [...]