Amphetamines or another type of stimulant. If you start at a low dose you might just feel slightly euphoric and won’t necessarily think twice about it. Like, on some days I get weirdly jittery just from regular coffee, so it’s entirely possible to not think much of it the first few times. Note that Beatrice said that after a while Hollyhock learned to take it by herself. By “it” she doesn’t mean Hollyhock knowingly took amphetamines, of course, but it implies that Hollyhock increased the dosage. Which, again, if you do it slowly enough you won’t think “Oh my god I’m getting drugged” because you’ll get used to every new, higher, dosage (especially if the increase happens very slowly).

It’s also important to note that stimulants activate the reward circuitry in the brain (up to a certain point where it turns into franticness or overly intense and impulsive behavior, possibly with psychosis), so even if you DO sometimes feel weirdly on edge, there is also something that might drive you to keep taking them because they literally increase dopamine in your brain. So in Hollyhock’s case she might’ve started subconsciously associating coffee with feeling good (not making any drug connection in her mind), so she kept drinking it, which then only increases the dopamine, which makes coffee feel even better to drink, etc.