Differential Diagnosis of Medication Intolerance

Has the patient stopped taking the drug because of intolerable adverse side effects?

Is the patient taking too high a dose, with dose-related toxicity?

Does the patient have a pharmacogenetic reason underlying the adverse effect?

Is a comorbid condition causing drug accumulation?

Is the patient experiencing a non-dose dependent adverse effect (allergy, other)?

Is the patient reacting to an excipient or additive used in the formulation?

Has the patient been given a counterfeit drug?

Is the drug interacting with another medication?

Is the patient experiencing immune reconstitution?

Is the patient complaining of a reaction that is the intended drug effect?