did-you-kno:

Couples who smoke weed together are
less likely to hurt each other. Studies of
husbands and wives during their first 9
years of marriage found that spouses
who both frequently smoked marijuana
were less likely to engage in domestic
violence than couples with only
one partner who smokes. Source Source 2 Source 3

I don’t know how you’d tell if this is actually causation or just correlation, but it’s interesting.