A team of European researchers is establishing a new benchmark for studying how medications affect mothers and their breastfed infants, aiming to fill a long-standing knowledge gap in maternal healthcare. The newly published clinical protocol sets a “golden standard” for lactation studies, with hopes of making future treatment safer and more informed for breastfeeding women.
The study, featured in BMJ Open, focuses on how medicines like prednisolone and metformin transfer from mothers to infants through breast milk. Prednisolone is commonly used to treat conditions like rheumatoid arthritis, while metformin is prescribed for type 2 diabetes. Both drugs are crucial for managing chronic illnesses, yet data on their safety during breastfeeding remains scarce.
Women are often asked to choose between treating their illness or breastfeeding their child,” said Mats G. Hansson, senior professor of biomedical ethics at Uppsala University and head of the two clinical trials. “That’s an unfair position, especially when the science isn’t there to guide them.”
A Scientific and Ethical Gap
Roughly 70% of women take some form of medication during pregnancy, but about 95% of those drugs lack reliable safety data for use while breastfeeding. Existing lactation studies often rely on outdated data from a limited number of cases, or estimates based on animal models and mathematical simulations.
“This lack of evidence is not just a scientific issue—it’s an ethical one,” Hansson said. “Doctors and patients are forced to make life-altering decisions with almost no reliable data.”
A New Approach
The new standard involves collecting and analyzing samples of both breast milk and blood plasma from mothers and their breastfed infants. By measuring the actual drug concentrations in these samples, researchers can better understand how medications pass from mother to baby—and what impact they may have.
Unlike older studies, the new protocol also involves long-term biobanking, allowing future researchers to revisit and expand on the findings. All participants give informed consent for their samples to be used in future, unspecified research.
European Collaboration and Infrastructure
The studies are being conducted through a network of clinical centers across Sweden and supported by BBMRI-ERIC, a European research infrastructure that manages breast milk biobanks. This positions the research as part of a broader initiative under the European project ConcePTION, which aims to generate reliable, long-term data on medication use in pregnancy and breastfeeding.
By building a European infrastructure, we’re creating a foundation for future studies,” Hansson said. “We want to make sure that the next generation of mothers has better answers.”
This protocol could become a model for how medications are tested for breastfeeding safety, helping healthcare providers offer clearer, evidence-based guidance for women who are navigating the challenges of motherhood and chronic illness.
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