u/Exciting-Quality919

I've read most of the books, currently wrapping up the saga. Something that's stuck out to me is I've heard the Witcher elixirs treated as Witcher only, poisonous to those who have not undergone the Trial of Grasses. Yet in the books, I've not seen a single mention like that. The Trial itself is treated a little vaguely, but it's the trial and not the elixirs otherwise that are treated as dangerous.

So I'm wondering, is the notion of the elixirs Witchers commonly use being deadly exclusively a notion of the games?