In a recent episode of Doctor Who ("Face the Raven"), the drug Retcon, is utilized to erase a character's memory of the previous day. I've previously seen this utilized by Jack Harkness, in Torchwood, to prevent characters from remembering that Torchwood exists.
When was Retcon first used to achieve this short term amnesia?
Retcon was introduced in Torchwood, and first appeared in the first episode, "Everything Changes"; Jack spikes Gwen's drink with it:
Jack: How's your drink?
Gwen: Have you poisoned me?
Jack: Don't be so dramatic. It's an amnesia pill. My own recipe, with a touch of denial and a dash of Retcon. Wake up tomorrow morning, you'll have forgotten everything about Torchwood. Worse still, you'll have forgotten me, which is kind of tragic.
Torchwood Season 1 Episode 1: "Everything Changes"
"Face the Raven" is its first (and, so far, only) mention in live-action Doctor Who. There is a reference to an "amnesia gas" in the 2009 animated special "Dreamland", which may be a prototype Retcon, but this isn't confirmed.
