Columbia subject headings:
Endorphins--Congresses.
Endorphins--Metabolism--Congresses.
Endorphins--Physiological effect--Congresses.
Harvard subject headings:
Opioids--Congresses.
Opioids--Metabolism--Congresses.
Opioids--Physiological effect--Congresses.
Princeton subject headings:
Opioids--Congresses.
Opioids--Metabolism--Congresses.
Opioids--Physiological effect--Congresses.