Medications incompatible with breastfeeding

The concern of mothers who often ask, “I have taken a medication that is incompatible with breastfeeding—how can I clear my milk of it?” and who are met with the simple advice, “Express the milk and discard it,” or “Pump and dump” remains a reality of our time. It is important to understand that the core issue lies in how medications enter breast milk. But is this advice truly effective? Providing such a simplistic answer to a complex question is, in itself, incorrect. To understand why, we must first explain how a medication enters breast milk.

The renowned scientist Thomas W. Hale, who studied the effects of medications on breast milk, clearly explains the process of drug transfer into breast milk in his scientific article “Drug Entry into Human Milk” and emphasizes that this process depends on six key factors.

He points out that the degree to which each medication enters breast milk primarily depends on its ability to dissolve in fats. Lipophilic substances—that is, those that are highly fat-soluble—penetrate more easily into the milk’s fat component and tend to accumulate there.

In addition, molecular size plays a significant role: medications with small molecules pass more easily through the mammary barrier, whereas larger molecules generally do not penetrate.

Hale also notes that the higher the concentration of a medication in the mother’s blood plasma, the longer its elimination from the body—and, correspondingly, from breast milk—takes.

However, this process is also influenced by the degree to which the medication binds to plasma proteins: the more strongly a drug binds to proteins, the smaller its free fraction, which reduces its ability to transfer into milk.

Alongside this, an important factor is the oral bioavailability of the medication, because a drug reaching the infant through breast milk will only have a systemic effect if it is absorbed in the gastrointestinal tract and not broken down there.

Finally, the duration of the process is also influenced by the drug’s half-life (t½): medications with a long half-life remain in the mother’s body for a longer period and, consequently, can be transferred through breast milk for an extended time. Thus, the transfer of a drug into breast milk depends not only on its physicochemical properties but also on the mother’s physiological condition and the pharmacokinetic characteristics of the medication.

The factors mentioned above explain the mechanism by which drugs enter breast milk. However, in clinical practice, a more critical question is determining the time it takes for the drug to be eliminated from the body and its level of persistence in the milk. Previously, we discussed how a medication enters breast milk. Now, another question arises: once a drug has entered the milk, how long does it remain there, and how is it eliminated from the body? This question becomes especially important for medications that are contraindicated during breastfeeding…

Researchers Anderson and Sauberan have attempted to answer this question in their scientific studies. Their research shows that a medication is eliminated from the mother’s body only gradually, as its concentration in the body decreases. In other words, as the level of the drug in the mother’s system declines, its amount in breast milk correspondingly decreases. According to these scientists, a certain period of time is required for a drug to be completely cleared from milk. This period largely depends on the type of medication, the rate at which it is metabolized in the body, and its ability to dissolve in fats—that is, its lipophilic properties, as noted by Thomas Hale. Some medications do not remain in the body for long and are eliminated within a few hours or days, whereas others, accumulating in fatty tissue, may persist in breast milk for a much longer period.

Anderson and Sauberan argue that most medications are transferred to the infant through breast milk in very small amounts and, in most cases, do not pose a danger. However, this amount may vary depending on the type of medication and the individual characteristics of the mother’s body. They emphasize that each drug has its elimination period, and until this period has passed, it is impossible to “clear” the milk of the medication.

Furthermore, the authors address the widely held recommendation among physicians and specialists to “express and discard the milk.” This is a mistaken approach: expressing and discarding milk does not reduce the amount of the medication in it and does not accelerate the drug’s elimination from the mother’s body. Expression is useful only for relieving breast engorgement and maintaining milk production. It has no beneficial effect on the level of the drug in the breastfeeding mother’s system.

To partially reduce the transfer of medications into milk and minimize risk, a mother may, whenever possible, adjust the timing of the drug intake to correspond with feeding intervals or slightly delay its administration. This does not mean stopping breastfeeding but rather selecting a more suitable time for taking the medication. It is also possible to use alternative medications with similar effects that penetrate milk less or are considered compatible with breastfeeding. The mother must inform her physician that she is breastfeeding and emphasize the importance of lactation for herself and her infant so that the physician can make a safe choice.

The scientist also emphasizes the importance of the medication’s form of administration. Drugs for external use, nasal sprays, and inhalation therapies are generally less risky, as they enter the systemic circulation to a lesser extent and, accordingly, have a lower likelihood of passing into breast milk. Medications taken orally or administered by injection can create higher concentrations in the blood, and therefore their transfer into breast milk is relatively more probable. When developing a treatment plan, this distinction must be carefully considered by the breastfeeding mother, her family, and, most importantly, the healthcare professionals responsible for her care.

Author: Hajar Piriyeva
Breastfeeding Consultant