Ipecac

Ipecac was a purple-tinted drug in liquid form which, when ingested, causes severe gastric distress in Humans. Ipacac is easy to conceal, and appears to dissolve very quickly in room-temperature liquids.

Ipecac was used by Doctor Julian Bashir to poison a drink in a holosuite program in Quark's on Deep Space 9, part of an elaborate ruse staged by station personnel to defeat a jack-in-the-box subroutine planted in the "Vic's lounge" holoprogram by its creator, Felix. 

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Ipecac