Hi

Nvm i went through the chapters and found what its purpose

Hahaha I need that soup ... not for me though .. for my useless family (cousins) who keep having babies without marriage or job

Uh damn.

It's birth control that's only given to guys, but as Butterfly explained it some women put aphrodisiacs in it if they want to punish the male for whatever reason and they just watch them suffer without relief. From my understanding women have no real use for so it may have some negative effects and the soup is given to concubines that you don't want to have children with so someone like Feng Yu whose a main consort from a noble family wouldn't be given such a thing...it would be a sign that he's unfavored by his wife if she gave him birth control.