Neoethylene was a type of drug compound used in 23rd century Federation medicine.

When the USS Enterprise was overrun with appeared to be "giant tribbles" in 2269, Doctor Leonard McCoy was able to remedy the situation by giving them "a simple shot" of neoethylene. As a result, the "giant tribbles", which were in reality tribble colonies with voracious appetites, broke down into their individual units with a slower metabolic rate. (TAS: "More Tribbles, More Troubles")

In chemistry, the term "neo" refers to a new chemical compound that is isomeric with a related compound. While neoethylene is a fictitious compound, based on the nomenclature, it could theoretically be described as having the same number of atoms as ethylene (C2H4), but have a different structural arrangement and properties.
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