In real life (as I understand it) when we are "in love" there are biochemical changes going on. I believe we do undergo a limited degree of changes in complexion, muscle tone, flushing in the cheeks and lips and other areas, as well as changes in the eyes and hair. If true then the venus drug does essnitially the same but to much greater effect. Certainly when aroused and stimulated parts of our body do become flushed as blood rushes to those areas which, of course, affects complexion.
As I suggested what we see on television could be taken as a heavy handed way of illustrating the idea of what could actually be happening. And if traces of the drug are already in someone's system then taking another dose could result in a faster or short reaction time to take effect.
Of course this is all just rationalization because there's a limit to how much they actually thought this through. Certainly we know in real life many people considered average in looks can be made much more appealing with a makeover in grooming and posture and attire. The Venus drug is basically doing this without having to go to a salon. But if Eve and the others had been taking this drug for some time and had become used to what they're supposed to feel like after taking the drug then Eve adopting the familiar behaviour (without thinking) after taking the placebo could account for a measure of how she comes across to the men present.
Again in real life a lot of a person's appeal can come from how they carry themselves. A lot of celebrities are really just average in appearance, but much of what they are comes from knowing how to carry themselves (with confidence) and how they groom and dress.
Another aspect of real life not to be overlooked is how often some very physically attractive people don't actually think of themselves as particularly attractive. Many people experience this where some small flaw they see in themselves looms much larger in their imagination then it does to others (if others even notice at all). Eve and the other women could have been of just average appearance yet in their own minds they thought themselves ugly when measured against what they each thought was genuinely beautiful.
We also don't really know much about the Venus drug. Are they any deliterious side effects particularly after repeated and long term use---maybe the real reason why it's illegal? How does it affect you when the "positive" effect starts to wear off? Does it leave you as you were or maybe even less than what you were?