Multiple realities
(covers information from several alternate timelines)

Chronexaline was a drug under development at Starfleet Medical in the year 2404, designed to protect biomatter from tachyon radiation.

In that year, Admiral Kathryn Janeway requested 2,000 milligrams from The Doctor, in order to protect her from the harmful side effects of the chrono deflector, a time travel-device which she subsequently used to travel to 2378 and change history, returning the USS Voyager to Earth sixteen years earlier than it would have without the admiral's intervention. (VOY: "Endgame")

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