These are types of poisons your OC can use or be affected with.
Strychnine
You know how in movies a person is poisoned and they start twitching and sputtering and foaming at the mouth? That is not true. Unless you are talking about Strychnine Poison. It makes your muscles twitch and your mouth foams as it slowly and painfully kills you.
Lowly Castor Bean
This bean is poisonous! It has the poison, ricin in it. When ingested, it can cause respiratory and kidney failure.
Cyanide
When exposed to it, you could literally die in minutes from seizers and/or heart attacks.
Sarin
But then we have Sarin, which is literally hundreds of times deadlier than Cyanide. One small smell of it can make you foam at he mouth, go into a coma, and die. Yes. One small smell. And it used to be a PESTICIDE until it was outlawed as a warfare agent in 1997.
Tetrodotoxin
Tetrodotoxin is found in pufferfish. When eaten, it can paralyze and kill you in less than six hours. Five Japanese people will die every day from eating badly made pufferfish, which is called fugu there. Would you eat something that is at risk of being painfully deadly?
Compound 1080
Used to kill animals, it's a little bit too strong. For up to a year, the bodies of animals killed with it are still poisonous. It is odorless, tasteless, water soluble, and it has no antidote. It blocks the cellular metabolism, giving you a swift yet excruciatingly painful death.