Medicine interaction describes a complication where the combination of more than one drug in the human body results in an additional side effect of the combination that would not be present, or would be less severe, if both drugs were not being used. One of the most common and dangerous interactions is alcohol with narcotics, where the depressive effect of both drugs is amplified. As a result, an overdose is more likely with concentrations well below what would normally be required for either drug alone.

In Alone, House correctly diagnoses that a patient with a fever who has been given demerol is suffering largely from an adverse reaction of that drug with the anti-depressants the patient had been secretly taking for her clinical depression.

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