Exogenous: Originating from without (the body). This term refers to hormones, enzymes, or other bioactive chemicals produced outside the patient's body and injected, ingested, inhaled, or introduced into the body in some other manner. The opposite of endogenous.

Any insulin that is injected is termed as exogenous, because it did not originate within that particular body. The term is not limited to injected substances. Steroids or other hormones given orally also are termed as exogenous.

Treatments given for conditions such as Addison's disease and hypothyroidism can be administered orally and are considered to be exogenous, either replacing or supplementing the endogenous, natural hormones of the body.

A common term used for the administration of exogenous hormones is hormone replacement therapy. That term also applies to the injection of insulin.

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