Those who took ecdysterone saw their performance improve by three times as much as those who did not.
"We saw drastic increases in maximum performance in bench press in the group that took ecdysterone," co-author Maria Parr, a doping researcher at the university's Institute of Pharmacy, told CNN via telephone.
The study was partly funded by the World Anti-Doping Agency (WADA), and researchers recommend that ecydysterone be included on the agency's banned list.
Co-author Francesco Botr, director of the Italian anti-doping agency (FMSI), told CNN that the team are now investigating ways to test for ecdysterone.
The agency has recently been embroiled in controversy over the September 2018 reinstatement of the Russian anti-doping agency RUSADA.