Implant GRX is a non-addictive drug with the same effects as turbo; it slows down your surroundings to give you more time to act. It is accessed from your inventory in the Aid section of your Pip Boy, with the supply replenished every 24 in-game hours. This perk can be taken twice, for enhanced effects:
Rank 1: it can be used 5 times a day, and lasts 2 seconds per dose.
Rank 2: it can be used 10 times a day, and lasts 3 seconds per dose.
The effects of multiple doses are cumulative.
With the Chemist and Day Tripper perks, rank 2 of Implant GRX will last 22.8 seconds in real time with each use. With Logan's Loophole, Chemist, and Day Tripper, the duration of each use (rank 1) is 30.4 seconds in real time.
The Fast Times perk does not affect Implant GRX duration.
Implant GRX uses do not accumulate over time. The number of remaining uses will always revert to the maximum (5 at rank 1, or 10 at rank 2) every 24 in-game hours.
Like all chems, the duration of Implant GRX will stack with multiple doses. This can result in a lengthy duration of slow motion by consuming many doses at once (up to 228 seconds in real time using all 10 doses with GRX rank 2, Day Tripper and Chemist).
Uses of Implant GRX are not removed when starting the Dead Money add-on.
Uses of Implant GRX cannot be hotkeyed.
The effects of the implant are not cumulative with the chem turbo. Doses of turbo taken at the same time will be wasted.
Behind the scenes
The name is an obvious reference to the opposing car, the GRX, from the two-part episode of Speed Racer "The Fastest Car on Earth."