Factitious diarrhea may be caused by the ingestion of a variety of laxatives. Stimulant laxatives can be detected using thin layer chromatography (TLC).


Stimulant laxatives:

(1) bisacodyl (Ex-Lax, Correctol, Dulcolax)

(2) anthraquinones

(2a) senna (Senokot, Castoria, Black Draught)

(2b) cascara


Usual screening method of detection: thin layer chromatography on urine or stool


Causes of a false negative test:

(1) intermittent use of the laxative

(2) single specimen tested

(3) testing only urine or stool (not both)

(4) use of senna (the metabolite Rhein is not detected at clinical levels by TLC)


False positive results for bisacodyl may occur, so a single positive result should not be used alone to make the diagnosis.


If the results of the TLC screen are in doubt, then alternative testing (HPLC, other ) should be performed.


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