Retcon

Retcon was a pill that would induce amnesia in anyone that took it. It was used by Torchwood 3 to keep their existence secret.

Suzie Costello gave retcon to Max once a week for two years. (TW: They Keep Killing Suzie)

Jack Harkness gave retcon to Gwen Cooper when they first met, but she later regained her memories. (TW: Everything Changes)

Gwen gave retcon to Rhys Williams after confessing her affair with Owen Harper. (TW: Combat)

Jack Harkness told Gwen to give Rhys retcon after he learned about Torchwood, but she refused. (TW: Meat)

The members of Torchwood 3 took retcon to forget Adam Smith, thus killing him. (TW: Adam)

Torchwood 3 gave retcon to the guests at Gwen and Rhys' wedding. (TW: Something Borrowed)