Chemically related to Ketamine, it is (or was) a research chemical having dissociative properties as wel as acting as a serotonine re-uptake inhibitor.
SSRI effect is heightened serotinine, which leads to:
- confidence is increased
- inhibitions are lowered
- problems seem smaller
Dissociative effect leads to:
- physical movement require more attention, however the focus on it can actually make one more supple and ballet-like, as well as quick.
- environmental cues such as sound seem strange - rather than hear the rustle of leaves you hear the sound of each individual leaf.
So in your story, the person being does with this... At a lowish dose they might not notice but the effect might not be strong enough for your plot device. A higher dose would be noticable, but due to the effect, might not be a problem, especially if the person has a positive belief about it.
Too much can be a problem for your criterion number two, as with too much you can literally check every bike in a rack and skip over yours because you don't recognise it, then walk away thinking it has been stolen.
Criterion three: this would definitely be detectable in a beverage as it's quite bitter.
I have another mention that I just thought of while trying to get around the bitterness problem.
It's called Scopolamine. It needs a very perfect dose, as just a little too much and it can become deadly, however it basically makes someone suggestible to the point of no defense, and they forget all about it when it wears off.
It's administered by blowing it as a powder into someone's face.
One thing that, again may become a plot snag for you, is that I don't think there would be a way to get your character to be suggestible only to you and not to anyone else - Ie I think they become suggestible to everyone. One possible idea might be to use an earwig and keep reminding them what they're supposed to be doing, but that seems convoluted based on your description, not to mention difficult to pull off in a competition.
Really cool question though - thanks to you I now also know there's a stack exchange for world building, which is a really cool thing on its own!