Differential Diagnosis of Medication Intolerance

Causes of adverse effects associated with a medication:

(1) too high a dose, with dose-related toxicity

(2) pharmacogenetics, affecting how the patient responds to the drug

(3) comorbid condition that causes drug accumulation

(4) non-dose dependent adverse effect (allergy, other)

(5) reaction to an excipient or additive used in the formulation

(6) counterfeit drug

(7) drug interaction

(8) immune reconstitution

Sometimes a patient may be intolerant because s/he misinterprets an intended effect as being an adverse effect.

Intolerance may be changed to tolerance by:

(1) reducing the dose

(2) finding a formulation without an offending additive

(3) change other medications or the timing of dosage administrations

Sometimes the adverse effect is transient and the patient has to be encouraged to persist in taking the drug despite the unpleasant effects.