[Katie]

There are probably many reasons, a sure one is that it provides a layer of abstraction that allows one to suspend beleif and protect denial.
you see, by taking Pharma Estrogen it`s almost a clear admission that you`re taking Female hormones, whereas a "herb" is a bit non descript and doesn`t really require the same level of acknowledgement.
One might even convince oneself that it`s "only a herb" and can`t possibly be effective (this happens a lot on some TS forums) thereby removing the ownership of the condition.

TLDR; it`s semi effective whilst allowing the protection of denial.