Medications During Lactation: Which Drugs Enter Breast Milk and Which Don’t?

Breastfeeding mothers often face a difficult question: what happens if I need medication? Many people worry that any drug taken by the mother will inevitably affect the baby through breast milk. This concern can lead to two common outcomes—avoiding necessary treatment, or stopping breastfeeding earlier than planned.

Current medical evidence, especially studies published between 2024 and 2026, paints a more reassuring and nuanced picture. Most medications do pass into breast milk, but usually in very small amounts. In many cases, these amounts are too low to cause harm. The key is understanding how this process works and how to judge risk in a practical, informed way.

Not “Safe or Unsafe,” but “How Much and What Kind”

Older advice often divided medications into “safe” or “unsafe” during breastfeeding. In reality, things are rarely that simple.

Modern guidelines, building on principles from the American Academy of Pediatrics and updated clinical research, suggest a different approach: weigh three things together—the mother’s need for treatment, the possible exposure to the baby, and the benefits of continuing breastfeeding.

One important fact helps put things into perspective: after a mother takes a medication, the amount that reaches breast milk is usually only about 1% to 5% of the level in her bloodstream. For many drugs, this is far below the dose that would have any effect on an infant.

How Doctors Estimate Risk

Instead of asking whether a drug enters breast milk (most do), clinicians now ask how much enters and whether that amount matters.

A commonly used measure is the Relative Infant Dose (RID). This compares how much drug the baby receives through milk to the mother’s dose. In general, if this value is below 10%, the risk is considered low. For drugs that affect the brain, a more cautious threshold of 5% is often used.

But numbers alone don’t tell the whole story. Another key factor is whether the baby can actually absorb the drug. Some medications may be present in milk but are broken down in the infant’s digestive system and never enter the bloodstream in meaningful amounts. This is why certain large or complex drugs, such as insulin or some newer biologic therapies, are considered compatible with breastfeeding.

Why Most Drugs Stay at Low Levels in Milk

Whether a drug enters breast milk depends on its physical and chemical properties. Drugs that are small, fat-soluble, and loosely bound to proteins tend to pass more easily into milk. Others, especially large or tightly bound molecules, remain mostly in the mother’s bloodstream.

Recent reviews highlight an important point: most medications do not have all the characteristics needed to transfer into milk in large amounts. This is one reason why clinically significant exposure in infants is relatively uncommon.

The Baby’s Condition Matters Just as Much

The same medication can have different effects depending on the baby.

Newborns, especially those born prematurely, process drugs more slowly because their liver and kidneys are still developing. This makes them more sensitive to even small amounts of medication.

In contrast, healthy infants older than about six months handle medications much more efficiently. In this group, side effects from drugs in breast milk are rarely seen in practice.

What Recent Studies (2024–2026) Are Showing

New research is helping fill gaps that existed for many years.

For example, newer medications for diabetes and weight management, such as semaglutide, have been studied using sensitive laboratory techniques. In a small 2024 study, the drug could not be detected in breast milk samples, and even conservative estimates suggested extremely low infant exposure—around 1% of the mother’s dose.

Similarly, newer treatments for postpartum depression, such as zuranolone, show very low transfer into breast milk, with relative infant doses well below 1%. However, because long-term data in infants are still limited, doctors often discuss options with patients, including continued breastfeeding with monitoring or temporary interruption.

These examples reflect a broader trend: instead of assuming risk due to lack of data, researchers are now measuring actual drug levels and making more precise recommendations.

A Practical Look at Common Medications

In everyday life, the medications most breastfeeding mothers encounter are for infections, pain, allergies, or chronic conditions. For many of these, the evidence is reassuring.

Antibiotics such as penicillins and cephalosporins are widely used and generally considered compatible with breastfeeding. Some babies may experience mild digestive changes, like loose stools, but serious problems are rare.

For fever and pain, medications like acetaminophen and ibuprofen are among the safest options. They enter breast milk in very small amounts and are quickly cleared from the body.

Cold medications deserve a bit more attention—not because they are inherently dangerous, but because they often contain multiple ingredients. Decongestants like pseudoephedrine, for example, may reduce milk supply, while certain antihistamines can make infants sleepy. Using single-ingredient medications when possible makes safety easier to evaluate.

Cough suppressants also vary. Dextromethorphan is generally considered low risk, but codeine is not recommended. This is because some individuals metabolize codeine more rapidly, leading to higher levels of active compounds that could affect the baby.

For chronic conditions, many commonly used medications are compatible with breastfeeding. These include drugs for high blood pressure such as propranolol or nifedipine, and for diabetes, metformin. In contrast, most chemotherapy drugs remain unsuitable due to their toxicity.

Herbal and “Natural” Remedies: Not Always Safer

A common belief is that herbal or traditional remedies are safer than conventional medicines. In reality, their safety during breastfeeding is often harder to assess.

Herbal products may contain multiple active compounds, and their composition can vary depending on how they are grown and processed. There are also concerns about contaminants such as heavy metals. Because of these uncertainties, reliable data on how these substances affect breastfed infants are often lacking.

For this reason, it is generally more cautious to avoid using herbal products without professional guidance during lactation.

Simple Ways to Reduce Infant Exposure

For mothers who need medication, a few practical strategies can help reduce the baby’s exposure without interrupting breastfeeding.

Taking medication right after a feeding is one commonly suggested approach. This allows time for the drug level in the milk to decrease before the next feeding. Choosing medications with shorter half-lives or simpler formulations can also make a difference.

In most cases, no special action is needed beyond observing the baby. Signs such as unusual sleepiness, feeding difficulties, rash, or digestive changes may warrant a medical review, although these reactions are uncommon.

Treating the Mother Is Part of Protecting the Baby

An important point that recent research continues to emphasize is that untreated illness in the mother can itself create risks.

For example, untreated infections may worsen or spread, unmanaged depression can affect bonding and caregiving, and poorly controlled chronic conditions like hypertension or diabetes can have long-term consequences.

From this perspective, appropriate treatment is not in conflict with breastfeeding—it is often part of supporting it.

Looking Ahead: More Data, Better Decisions

Large ongoing studies in Europe and the United States are collecting detailed information on how medications transfer into breast milk and how infants respond. These studies aim to replace uncertainty with clear data, making future recommendations more precise.

As this field develops, the direction is clear: decisions about medication during lactation are becoming more individualized, based on real measurements rather than assumptions.

Conclusion

Most medications taken during breastfeeding do pass into breast milk, but usually in small amounts that are unlikely to harm the infant—especially if the baby is healthy and older.

Instead of avoiding medication out of concern, a more balanced approach is to understand the type of drug, the amount that reaches the milk, and the condition of the baby. With this information, many treatments can be used safely while continuing breastfeeding.

In many situations, addressing the mother’s health needs is not separate from protecting the child—it is part of the same goal.

References:

[1] U.S. Food and Drug Administration (FDA). (2024). Medication safety in breastfeeding: Updated guidance. https://www.fda.gov

[2] European Medicines Agency (EMA). (2024). PRAC recommendations on medicines during lactation. https://www.ema.europa.eu

[3] Anderson, P. O., & Sauberan, J. B. (2023). Modeling drug passage into human milk. Clinical Pharmacokinetics, 62(4), 453–468. https://doi.org/10.1007/s40262-022-01185-6

[4] Sachs, H. C. (2023). The transfer of drugs into human breast milk: An update. Pediatrics, 151(2), e2022058800. https://doi.org/10.1542/peds.2022-058800

[5] National Library of Medicine. (2025). Drugs and Lactation Database (LactMed®). https://www.ncbi.nlm.nih.gov/books/NBK501922/

Author Information

This article was written by Dr. Alistair Vaughn Mercer, a medical content specialist focusing on clinical pharmacology and maternal–child health. Dr. Mercer has extensive experience interpreting drug safety data, including pharmacokinetics, lactation exposure studies, and real-world clinical evidence. His work centers on translating complex medical research into clear, practical guidance for general audiences while maintaining scientific accuracy. He contributes to evidence-based health platforms and emphasizes responsible communication aligned with current clinical guidelines and European Association for Drug Education and Training Standards.

Disclaimer

This content is for informational purposes only and does not replace medical advice. Medication use during breastfeeding should be discussed with a qualified healthcare professional, taking into account individual health conditions and the most current clinical evidence.