Can the human body make this molecule? If the body cannot make this molecule, what is its source? (Where does it come from?) Is it an essential nutrient? (In ssential nutrient? (in your answer. define what an essential nutrient is.) Is it a drug? Explain your answer. (One definition for a drug is "any absorbed substance that changes or enhances any physical or psychological function in the body." You may wish to explore other definitions of "drug". In your explanation for this question, you should state which definition of "drug". that you are basing your answer on.) If this molecule is made by the body or is an essential nutrient, what body system uses it and what is its function? If this molecule is a drug, what system does it act on, how does it work, and for what purpose?