Why do happiness drop so much? I have had girls at 300 at night and next day it is down to 180.
From what I understand there is a base happiness value that can be changed by serums that have permanent happiness changes, otherwise it should revert to the mean overtime. Not sure though.
Broadly speaking, serum effects that are just "+ Whatever to Something" are temporary and will be
subtracted from that stat's new value when the serum effects expire. Serums that either explicitly state "Permanent + Something-or-other" or "+ Somesuch/turn" are permanent (but only become available gradually).
So e.g. the Slow Release Dopamine gives a permanent +5 to happiness per turn for as long as the serum lasts, which is pretty neat.
But the Distilled Aphrodisiac gives a temporary +15 to Sluttiness for as long as the serum lasts
up to the stat maximum, but then subtracts those 15 from the stat when the serum expires. So if the_person had say 90 Sluttiness before, the serum will temporary bump it up to to the max of 100, but will then subtract 15 from the 100 on expiry, taking it down to 85.
Other than that, maybe the_person just hates their job? If they hate the uniform policy, the specific task they're given, and working in general, those malus'es will pile up. Sometimes it's worth using a few trances to make sure they love what they're doing, if you can't rely on serum control alone.
At least that's how I understand it, but note that I haven't kept up with the latest releases (generally only begin a new playthrough every few years because of the save issues).