This while I have no issue with the drug thing for other characters the way Rika is with them makes me think it will turn her into a addict rather easily. I rather not have that will ruin her character for me be one thing if she started as one or had some addict traits but she doesn't.It will be potentially disastrous if the Dev exposes her to pills and such. When women are drugged it automatically becomes rape (legally). So all consent and mutual understanding between her and the MC goes out the window. And should she take it herself, she will still no longer be herself, therefor her decisions wont be her own. It's funny to see games try to rationalize it as lust enhancer or libido booster. But there is no way around it, a chemically altered brain is no longer under ones own control. I for one would prefer to see Kat keep getting naughty by her own free will.
Now about her getting drugged im mixed on that subject. On one hand I like the dark tone this game has, sure it doesn't need it but I cant deny it wouldn't be fitting with the dark tone this game has. However id hate to have something bad happen to Kathryn and I rather Kathryn not have sex cause she is drugged up but of her own free will like you said. I think the drug thing needs to be a choice if Kathryn is going to have sex while on something. But if it's used to lets say incapacitate her for some reason and not have sex with her , I think id be okay with that not being a choice as it does match this games dark tone.