2C-EF-FLY is a psychedelic drug of the phenethylamine, 2C, and FLY families. It is the FLY (benzodifuran) derivative of 2C-EF and is a fluorinated derivative of 2C-E-FLY. The in-vitro metabolism of 2C-EF-FLY and its monoamine oxidase (MAO) interactions have been described. 2C-EF-FLY produces the head-twitch response, a behavioral proxy of psychedelic effects, in rodents. It showed around half the potency of 2C-B-FLY and 2C-E-FLY in this assay, but was slightly more potent than 2C-I-FLY. 2C-EF-FLY was first described in the scientific literature by Lea Wagmann and colleagues in 2018 or 2019. It has been described as a novel designer drug.