The present invention provides methods of treating or preventing at least one of postnatal depression (PND) and postnatal anxiety (PNA), and risks and sequelae thereof, by administering Lactobacillus rhamnosus HN001 or derivatives thereof, in addition to uses, compositions, and medicaments comprising Lactobacillus rhamnosus HN001 or derivatives thereof to treat or prevent at least one of PND and PNA, and risks and sequelae thereof.