Willow (Salix sp.) bark contains salicylic acid and its derivative salicin. Willow bark has no specific lactation-related uses. It is traditionally used to treat fever and inflammatory conditions, but it also is found in some weight loss products. After salicylate or salicin ingestion, salicylic acid is excreted into breastmilk. The excretion of salicylate into breastmilk increases disproportionately as the maternal dosage increases. Long-term, high-dose maternal aspirin ingestion probably caused metabolic acidosis in one breastfed infant. Reye's syndrome is associated with aspirin administration to infants with viral infections, but the risk of Reye's syndrome from salicylate in breastmilk is unknown. Willow bark is best avoided during breastfeeding. Safer drugs are available for pain and fever.
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