Men whose wives earn more income are more likely to use erectile dysfunction medication than those who outearn their wives, even when the inequality is small, according to a new study. Researchers looking at more than 200,000 married couples in Denmark from 1997 to 2006 also found that wives who outearned their husbands were more likely to suffer from insomnia and to use anti-anxiety medication.

They did not find these effects for unmarried couples or for men earning less than their wives prior to marriage.

The finding appeared online in Personality and Social Psychology Bulletin.