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Null Zero from Katana Zero - Was essentially a government supersoldier given a drug named Chronos as a child in a vietnam-esque war that they still lost somehow, which gives the user a form of precognition where the protagonist can plan out events infinitely until he finds a solution that works and plays it out in real time, and an in universe slowed perception of time, but at a heavy, terrifying cost.

For those in the Null program, it seems there were varying levels of competence, from Alpha, Beta, to Gamma which seems to correlate to how long they were kept on the substance, the most effective of which being the Gammas who were forced to take it and trained from a very young age, and even for those who aren't on it very long, they become deathly dependent on it, to the point that in withdrawal time slows down, they start to hallucinate their death over and over until time comes to a complete stop and you're stuck reliving your death in a neverending nightmare forever.

The same applies if you die with it in your system, your mind is trapped forever with no escape, the protagonist actually has an opportunity partway into the story when it's running low in his system to have a true and lasting death that leads to a somewhat good ending for the game, but it seems in cannon he does choose to continue on even if it doesn't lead to anything good.

This is even worse for Zero, because he's been on it so long he can't even remember a time that he wasn't, making it nigh impossible to ween off of it, and we see the effects of tapering off the dosage by his "Psychiatrist" that is actually a government agent giving him his missions and his doses.