Can Maternal Urine or Saliva Predict THC in Breast Milk?
Maternal urine and saliva did not consistently track breast-milk THC across early postpartum sampling. A small observational study found correlations at the first assessment, but not at later assessments, making one matrix an uncertain substitute for another.
Three specimens, two analytes
Sandonís and colleagues followed 13 postpartum women with cannabis-positive urine at delivery. Samples were collected at approximately 24 hours, 48 hours, and one week after birth. LC–MS/MS measured parent THC in milk and saliva and THC-COOH in urine.
Those are different matrices and different analytes. Urinary THC-COOH is an inactive metabolite; it is not a measurement of parent THC in milk or an infant’s absorbed dose.
What changed over the first week?
Among participants who remained abstinent, milk THC declined and was below quantification at the one-week assessment, while urinary THC-COOH remained quantifiable. Salivary THC was often below quantification. Significant early correlations did not persist at the later stages.
The result therefore does not support treating a maternal urine concentration as a fixed multiplier for milk THC. A correlation in a small group at one time point is not an individual prediction rule.
Why this is not a universal clearance deadline
The cohort was small and selected, sampling was limited, and the findings depended on cessation and the assays’ quantification limits. Below quantification is not proof of zero analyte at every time or of zero infant exposure. The study did not establish a universally safe interval for breastfeeding or determine long-term infant outcomes.
Interpretation should also use the corrected publication. The authors issued a correction to descriptive neonatal urine toxicology data; the correction states that the study’s results and conclusions were unchanged.
How to assess a specific result
Identify exactly which analyte was measured, in which specimen, at what time, and against which reporting limit. Establish the maternal exposure history rather than assuming continued use or abstinence from one result alone.
The study informs matrix-specific interpretation. It does not authorize replacing individualized clinical assessment with a positive maternal screen, a single saliva result, or a one-week calendar rule.
For related context, see our discussion of why urine and blood drug results are not interchangeable.
Primary research
Miguel Sandonís; Maia Brik; Clara Ramirez; Laura Castellote; Anna Creus; Gemma Parramón; Anna Suy; Josep Antoni Ramos-Quiroga; Raul Felipe Palma-Álvarez; Constanza Daigre. Breast milk Δ9-tetrahydrocannabinol in cannabis users during the postpartum period: correlation between breast milk, maternal urine and saliva samples during early lactation. Frontiers in Psychiatry (2026). DOI: 10.3389/fpsyt.2026.1816611.
Published correction: Corrigendum: Breast milk Δ9-tetrahydrocannabinol in cannabis users during the postpartum period (2026). The correction addresses descriptive neonatal urine toxicology data and states that the results and conclusions are unchanged.
