It may be the RESULT OF PRESCRIBING CERTAIN DRUGS to the patient with the INTENTION TO PRODUCE A SPECIFIC DEGREE OF ACTION BUT the nature of the INTENSITY OF THE ACTION PRODUCED IS DIFFERENT FROM that INTENDED by the prescriber. UNDESIRABLE PHARMACOLOGICAL INTERACTION between two or more ingredients that leads to: -POTENTIATION of the therapeutic effects of the ingredients - DESTRUCTION OF THE EFFECTIVENESS of one or more of the ingredients - occurrence of a TOXIC MANIFESTATION within the patient