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")