Excellium was a drug made by Blind Summit from data supplied from Torchwood One by Matthew. Said data originated from the Brett Archive.

It could create super-soldiers, although the rejection rate was very high. Pascal Babich used it on the homeless and desperate. Ianto Jones volunteered in order for Yvonne Hartman to learn about Blind Summit's plans. It inadvertently returned all Ianto's retconned memories. (AUDIO: Blind Summit)

Yvonne kept excellium. She had Kara use some on Dave Cooke to restore his original core memories. (AUDIO: Locker 15)

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