Chocolate.

Chocolate contains small amounts of caffeine and larger amounts of the closely related compound, theobromine. It also contains anandamide and two related compounds that stimulate cannabinoid receptors, tryptophan, and polyphenols.[1][2] All of these compounds are detectable in breastmilk in small amounts. Low intake of chocolate by a nursing mother is not problematic, but extreme amounts can affect the infant.