Paradoxical reaction

A paradoxical reaction is when medical treatment, usually a drug, has an opposite effect to an effect normally expected.

An example of a paradoxical reaction is when a pain relief medication causes an increase in pain. Some sedatives prescribed for adults, actually cause hyperactivity in children.

Benzodiazepines, a class of psychoactive drugs called the "minor" tranquilizers, have varying hypnotic, sedative, anxiolytic, anticonvulsant, and muscle relaxing properties, but they may create the exact opposite effects. Susceptible individuals may respond to benzodiazepine treatment with an increase in anxiety, agitation, aggressiveness and even convulsions. Paradoxical effects of benzodiazepines appear to be dose related, that is, likelier to occur with higher doses.

Chlorpromazine, an antipsychotic and antiemetic drug, which is classed as a "major" tranquilizer may cause paradoxical effects such as agitation, excitement, insomnia, bizarre dreams, aggravation of psychotic symptoms and toxic confusional states.