First let us talk about Hormone system...
It is anetwork of glands that signals the organ to produce/secrete hormones."Hormones"are the body's chemical mediatorsthat flows through our blood stream totissues andcontrols most of our body's major organs.
Some people are having problem to secrete its hormone because of some cases like Diabetes or hormonal imbalance in women.
Diabetes, is the case wherein the body doesn't produce insulin, when sugar/glucosein the blood can't be absorb properly because of the absence of insulin;Insulin helps the glucose to get absorb and used as energy. Since, there is an absence of insulin external introduction is needed socan beutilized.
Hormonal imbalance in women, some women having trouble in their mensturation / child-bearing because of some points. Right amount or defiency would affect the female reproductive sytem BIG TIME!
To wrap it up, absence of specific hormone need external help so it would function on its desirable role though some has some risk. For best results, hormone should be tailored individually and re-evaluated often to be sure its benifits and counterbalanceits venture!