In some individuals, drugs cause an inflammatory reaction which can induce the so called 'postinflammatory hyper-pigmentation'. It's a non-specific reaction leading to pigmentary changes. Some examples of the most common drugs associated to oral pigmentation are: Cotrimazole, tetracycline, arsenic in combination with sulphydryl groups, phenothiazines, minocyclines and many others have been implicated.
Typically the pigmentation shows a slate brown color and is more often seen in dark-skinned people.
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