Final answer:
The substances naturally produced by endocrine glands and which may also come in synthetic forms for medical use are known as hormones.
Step-by-step explanation:
Substances that are naturally produced in the body by endocrine glands, and which may also have synthetic equivalents prescribed for a variety of disorders, are known as hormones. These chemical messengers are secreted directly into the bloodstream and affect cells that contain receptors for them. Unlike neurotransmitters, whose effects are localized, hormones have widespread effects throughout the body. Hormones are categorized into different classes based on their chemical structure, including those derived from amino acids (like epinephrine and norepinephrine) and those derived from lipids (like steroids).