They provide a sense of wellness following exercise. They help us deal with
normal pain. In some circumstances they allow us to get through very painful
situations and continue to function briefly (as in some instances of shock).
They relax vessel walls under certain circumstances where it can benefit our
health, especially as regards heart attack risk during/following exercise
(1). 

However, one problem is that they are thought to cause the down regulation
of natural killer cells, which is the body's first line of defense against
malignancy (2) and some infections (3).  This is by no means a comprehensive
discussion of benefits and detriments of opioids and opioid receptors. :-)


Sources: 
1.
http://mdsports.wordpress.com/2007/11/28/endorphins-and-opioids-released-dur
ing-running-protect-against-heart-attacks/
2. Hoggan R. Considering wheat, rye, and barley proteins as aids to
carcinogens.
Med Hypotheses. 1997 Sep;49(3):285-8.
3. http://scienceweek.com/2005/sc050114-2.htm


Ron Hoggan, Ed. D.
co-author Dangerous Grains ISBN: 978158333-129-3 www.dangerousgrains.com 
author Smarten Up! ISBN: 978-0-9736284-3-2 www.smartenup.info           
editor: Scott-Free Newsletter www.celiac.com

"Objectivity is the prerogative of objects."