Cannabis use on a regular basis by breastfeeding mothers concerns me. Cannabis has a long half life (25-57 hours) and it takes 5 times this to be removed from milk. THC crosses the blood brain barrier and it is known to accumulate in body fats. Although it is highly protein bound and subject to first pass metabolism, the milk plasma ratio is 8. We do not know enough about the impact on the developing brain to be sure that the amount passing through breastmilk is safe. Regular use is not recommended in the breastfeeding mother or other members of the family who may expose the baby through passive inhalation.