My protagonist takes a drug every day that dulls his emotions, because his emotions are a weapon that an otherworldly entity built into him
In my Abaddon Cycle series (military/cosmic sci-fi, book 1 of 5 out), my POV protagonist Jason has "Abhamic powers" -- psychic abilities tied to emotional intensity. The stronger he feels something, the more dangerous he becomes to everyone around him, because he can't easily control his power...and the entity who 'gifted' this power to him is after his mind and soul. Jason is an unfinished test subject in a hostile world.
Jason didn't choose this: he, his brother, and Sam (pictured) were given these Abhamic abilities through repeated nanite exposure in a government laboratory setting, before they escaped. The lab and the nanotech both trace back to the same artifact: the Abaddon Beacon, a strange obelisk that was under study in the labs. The mystery of what Abaddon is, where it came from, and what it plans to do with the human race is a central first-book question...as well as whether the scientists were in control of the lab operations, or Abaddon itself.
But Abaddon isn't after his friends, only Jason. The reason why is another mystery. The 'chosen one' trope semi-applies here, but it's the series villain who chose him, not the universe or God or anything like that.
Abaddon is also the source of the Nanophage: a strain of its miraculous nanotech that can infect humans and machines, which has been happening more and more often as its technologies spread further and further into human society. It has been spreading through both primary factions of the story for years, despite attempts to slow it down. The Phage has a lot of purposes, but a big one is to allow Abaddon to project influence through it, at range. The Nanophage becomes the obelisk's eyes and ears in an ever-increasing radius (across the Sol System at the time of the story's beginning). So Jason can be ambushed by Abaddon's presence anytime, through a Phage-compromised laborer, a corrupted robotic unit, anything infected can become a conduit.
Jason's drug suppressant: Osmium
Osmium (not the metal) is the name of the neural suppressant Jason takes daily. It doesn't grant power or shield him physically; it flattens his emotions, same tradeoff as real-world drugs that dull your mind to manage a condition. Lower highs, higher lows, fewer feelings sharp enough to trigger a cascade, or Abaddon's notice. It works, but it costs him, bc Jason's not fully present in his own life--and his friends know this. But this keeps him under Abaddon's psychic radar.
If one of Abaddon's possession probes lands, or Jason misses an Osmium dose, or his control cracks, he loses control. Jason's abilities go into an automatic, indiscriminate defensive cascade that doesn't distinguish threats from bystanders. The only way to stop it is getting Osmium back into his system before his psychic outbursts burn through everything/everyone nearby. He's mostly a danger to others in these moments, not himself -- unless Abaddon's possession attempt actually succeeds, which is a different, WAY worse problem tied to what the obelisk ultimately wants him for.
Why I built the system this way
Magical powers, psychic powers and other stuff like that are super cool staples of the SFF genre, but these things have been done many times before. I thought that starting Jason off below where most protagonists start would be interesting -- BELOW the ability to even control himself, with that forming the core of his arc in the first book. Rather than training sequences with master Yoda, we see Jason gradually begin to get control over himself (and his outbursts), over the course of his journey to find Abaddon and stop it from doing whatever nefarious shit its trying to do.
There's a lot of focus on Jason's emotional state as he faces threats in the physical world, plus being under constant threat from an eldritch entity that can strike almost anytime. There's parallels to real-world forms of mental illness, anxiety attacks, panic spirals (which we're all familiar with, to some extent). Jason's struggle to overcome both himself and the entity that seeks his soul is the emotional core of the story, but once he's over that first hurdle, that's only the first stage of his development. There's way more to come in future books as Jason and his friends learn more about Abhamic abilities as they go--which is vital, because if they can't or they're too slow, Abaddon's ruinous plans for the human race will come to fruition.
Concept art attached is from an in-development graphic novel adaptation that I'm working on alongside the main series--different medium, not the novel's canon style, but it captures the moment better than I could describe it.
Happy to answer questions or comments about the Abhamic "magic" system, Abaddon, the Nanophage, or Osmium. Hit me!
(From "The Call of Abaddon")