Imperial Conditioning was a development of the Suk Medical Schools. It was the highest conditioning against taking human life, which meant that a Suk Doctor who had this conditioning could even serve an Emperor.
Initiates were marked by a diamond tattoo on the forehead and were permitted to wear their hair long and bound by a silver Suk ring.
The conditioning against taking human life had remained a stalwart of the Suk school for millennia. However, a way was found by House Harkonnen agent Piter de Vries to break this conditioning. De Vries realised that a person, even a Suk doctor, could be made to do another's bidding if one of their loved ones was held hostage. In this way, he was able to control Wellington Yueh into betraying his Duke, Leto Atreides, and deliver him to Baron Vladimir Harkonnen.
Though Suk Doctors continued to exist even into the time of Leto Atreides II and later amongst The Scattering, it could be surmised that the Suk School lost much of its prestige from this time onward or that their Conditioning was considered ineffective at the very least.