Denaxian tapeworm

From Memory Alpha, the free Star Trek reference.

The Denaxian tapeworm is a parasitic organism that attaches itself to the lower intestinal tract and absorbs nutrients from its host. Extracting it is a simple procedure that requires the insertion of a standard V-probe into the body.

Phlox used one as a "perfectly harmless" way to lose weight in late 2153/early 2154. (ENT: "The Council")