A landmark 2006 study published in the Lancet, which highlighted the risk of opioid overdose in babies breastfed by codeine-using mothers, is facing demands for an investigation. Calls for the paper to be reviewed came after a member of the original research team pointed out alleged misconduct by the senior team. The study was led by pharmacologist Gideon Koren at SickKids Hospital in Toronto. The Lancet issued a statement of concern over the article and called for a formal investigation. The reason for increased attention arose after it was discovered that a separate case report describing an overdose in a child, which was supposed to support the hypothesis of the Lancet study, was completely fictitious. This case report was allegedly published in a non-existent journal. These circumstances call into question the reliability of the guidance on codeine and breastfeeding that has been based on this study thus far.