128543
Endogenous anandamide is present at very low levels and has a very short half-life due to the action of the enzyme fatty acid amide hydrolase ( FAAH ) , which breaks it down into free arachidonic acid and ethanolamine .
 half-life
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: media, plant, vehicle, astronomical object, time, disease, animal, location, person, organization, mythical figure, food, biology, geographical phenomenon, instrument, event 
Text: {0} 
Answer:
 half-life