Fiona and others,

The soporifics are at least two: beta-casomorphins are peptides in the caesin
part of the milk. Cow millk is very high in caesin (80:20% - remember
cow=caesin, whey=women) and the specific beta casinomorphin that is a natural
opiate is 30 times more potent in cow than human.  Peter Hartmann's talk
"Breastfeeding: Past, Present and Future" from ILCA 1990 goes into this
concept in detail, and it's fascinating!

Tryptophan, another amino acid in milk, is a soporific when heated. That's
why a glass of warm milk at bedtime might help you sleep.

Speculating some more....

We know that opiates cause a rise in prolactin in the user.  I wonder how
much the craving for another "hit" of opiates is caused by a craving for a
prolactin-fix? And how much our need to breastfeed our babies and "mothering
instinct" is a need for a prolactin fix?  What does caretaking do to our
prolactin levels - is this why the night-shift tries to compete with mothers
to hold babies- to get their prolactin fixes??

Is this partly responsible for repeat pregnancies in non-breastfeeding teens
- a repeat pregnancy being a way to get a prolactin-fix without
breastfeeding?

Could this be cow's milk is an "addictive" allergen?  How many other
allergens trigger cravings?

Comments, anyone??
Linda Smith in dairy country in Ohio