Since the active ingredient in cannabis (marijuana, pot, etc.)-THC (TetraHdroCannabinol)-is fat soluble, accumulate in breast milk. For a suckling infant, this can have serious consequences.
Lactating women should generally avoid all forms of intoxicants, since these changes into the milk. Drugs can have a negative effect on milk production, milk volume, the composition and the secretion of breast milk. But first and foremost can drugs have a direct adverse effect on the infant. Any intoxicant, which can lead to a newborn will be dull/drowsy, can contribute to sudden infant death.