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Drugs in Breast Milk


By Christina Johnson   |   November 07, 2014

“Breast is best.” It’s an aphorism with a message blessed by no less than the American Academy of Pediatrics and World Health Organization, both of which recommend six months of exclusive breastfeeding for all infants.

But should a woman breastfeed if she is taking medications, either over-the-counter or prescription?

nursing infant

“In most cases, yes,” said Philip Anderson, PharmD, a clinical professor with Skaggs School of Pharmacy and Pharmaceutical Sciences at UC San Diego. “Your baby is much more vulnerable during pregnancy.”

Breast milk typically has only 1 to 2 percent of the dose that the baby would have received in-utero, he said.

In addition, most adverse drug reactions occur in infants younger than two-months-old. By six months of age, babies can metabolize and excrete drugs as well as adults, relative to their body size, said Anderson, who created LactMed, the National Library of Medicine’s database on drugs and other chemicals in breast milk.

Still, some common drugs in home medicine cabinets should be avoided while nursing, starting with aspirin.

Aspirin is linked to Reye’s syndrome, a rare but serious condition associated with swelling in the brain and liver of young children, he said. It can also thin the blood and cause bleeding.

Another to avoid: Naproxen (Aleve) in infants younger than two months. Because the drug lasts a long time in the body, it can accumulate in a newborn’s bloodstream. Safer alternatives to aspirin and naproxen include acetaminophen (Tylenol) and ibuprofen (Advil, Motrin). Both are excreted into milk in negligible amounts.

Cimetidine (Tagamet), a treatment for heart burn and acid indigestion, is another non-prescription drug to avoid while breastfeeding.

“Quite a bit gets into the milk and it can cause enzyme inhibition in the liver,” said Anderson, who is also the founding director of the Drug Information Service at UC San Diego Health Department of Pharmacy. For a safer alternative, he recommends famotidine (Pepcid).

Besides infant safety concerns, some medications can interfere with lactation. In one small study of eight nursing moms, cited on LactMed, a single 60 milligram oral dose of the common nasal decongestant pseudoephedrine (Sudafed) reduced women’s milk production by an average of 24 percent.

“Most drugs are transferred to breast milk,” said Christina Chambers, PhD, a professor of pediatrics and director of clinical research for the Department of Pediatrics at UC San Diego. “It is more a question of how much.”

“When it comes to breast milk, very little proactive rigorous research has been done to document the effects of drugs in breast milk on infants,” she said. “One reason for this is that these studies are not required for FDA approval of a drug. The accumulated evidence, however, is that most drugs are compatible with breastfeeding.”

UC San Diego has recently opened a breast milk repository that is collecting 50 milliliter samples of breast milk from volunteers. The samples will be analyzed to better understand breast milk’s unique biochemical properties and to document environmental toxins and drug residues in breast milk. Researchers are especially interested in documenting the presence and concentrations of drugs that could be harmful to infants in neonatal intensive care.

Trust your maternal instinct if you think something is wrong with your baby.

“Mothers are the best observers of what is happening with their babies,” Chambers said. “If a mom notices a change in her baby after she starts taking a new medication, contact a pediatrician immediately, and it’s a given that moms should go over all the drugs they are taking, including herbs and supplements, with their physician.”

When do drugs preclude breast feeding? Some radioactive drugs (given for diagnostic purposes or to treat thyroid conditions) and cancer chemotherapy drugs are examples. Other prescription drugs that should be used with caution in neonates include codeine, an opiate painkiller metabolized via what is known as a CYP2D6 pathway.

Some people carry a gene variant that makes them “ultra-rapid metabolizers” of codeine. Infants who carry the CYP2D6 gene variant and whose bodies are still slow at clearing drugs may be at high risk of serious toxicity effects. People of North African, Ethiopian and Saudi Arabian descent are most likely to carry the gene variant, while Chinese, Japanese and Hispanic people are among the least likely. Other opiate-derived pain killers should also be limited to a few days of use.

One more caveat to nursing moms: Scientists have yet to study the cumulative effect of multiple drugs on infants. There is also no rigorous data on the safety of herbs. “Women are on their own here,” Anderson said.

In California, free counseling about breast feeding and drugs in breast milk is available by calling 866-626-6847 for English and Spanish speakers.

Volunteers interested in donating samples of breast milk for the UC San Diego breast milk repository may contact Kerri Dutcher, at 858-246-1713 or by email at New mothers with questions or concerns about nursing, particularly for premature infants, can contact the Supporting Premature Infant Nutrition (SPIN) program or email

Related Specialties

Pregnancy and Childbirth