First, try not to take things too seriously.
The drug is both. It affects people slightly differently. What the MC gives girls in town is a less potent form of it. Once they come to the mansion, they are given the full dose. The specifics are intentionally left vague to allow flexibility in how different characters react (quickly or slowly) / (like an addict needing more and more or simply more open to intimacy with each dose).
As far as grinding money, at the very start of the prologue, the "Quick Introduction..." states "NOTE: In this game, there will be no grinding for stats or cash (the most you'll need is $10k). Try not to take anything too seriously."
I know those who skip the prologue may have missed this, and I suspect a few people may have skipped reading the Quick Intro text altogether. It's fine, but please understand we've tried to make LTA a no-grinding game (except for pelvises - grind those all you like)...
We get it. There are games similar to ours where you literally must grind out pennies to get enough in order to proceed. I've played some where I hold the CTRL button to skip about 75% of the time to fly through repeat grinding scenes. We wish to avoid that in LTA as much as possible.