Taking Medication While Breastfeeding: What You Need to Know

How does medication get into breast milk?

Almost all medications pass into breast milk to some degree, but the amount is what matters clinically. Medications enter milk primarily through passive diffusion from the bloodstream — the concentration in milk roughly tracks the concentration in maternal plasma 1Ref 1Verstegen RHJ, Anderson PO, Ito S (2022).Infant drug exposure via breast milk.Pharmacokinetic factors determining drug transfer into breast milk; RID concept; clinical significance of low-level exposure; immature infant drug clearance in newborns. The key factors that determine how much reaches the milk include:

• Protein binding: Highly protein-bound drugs have less free drug available to diffuse into milk.
• Lipid solubility: More lipid-soluble drugs enter milk more readily.
• Molecular weight: Very large molecules (such as biologic agents like monoclonal antibodies) transfer poorly.
• Oral bioavailability: Even if a drug is present in milk, if the baby cannot absorb it from the gastrointestinal tract, the effective exposure is low.
• Drug half-life: Longer half-lives mean the drug may accumulate across multiple feeds.

The standard clinical measure is the relative infant dose (RID) — the estimated dose the baby receives through milk as a percentage of the weight-adjusted maternal dose. An RID below 10% is widely considered the threshold for clinical acceptability 2Ref 2Spencer JP, Thomas S, Trondsen Pawlowski RH (2022).Medication Safety in Breastfeeding.RID <10% threshold; timing doses after feeding to minimize exposure; LactMed as authoritative free resource; sertraline as preferred SSRI with low RID; characteristics of safer medications (low oral bioavailability, high protein binding). Most commonly used medications fall well below this threshold 1Ref 1Verstegen RHJ, Anderson PO, Ito S (2022).Infant drug exposure via breast milk.Pharmacokinetic factors determining drug transfer into breast milk; RID concept; clinical significance of low-level exposure; immature infant drug clearance in newborns3Ref 3Sachs HC; Committee on Drugs (AAP) (2013).The transfer of drugs and therapeutics into human breast milk: an update on selected topics.Only a small proportion of medications are contraindicated during breastfeeding; many mothers receive unnecessarily restrictive advice; codeine contraindication; referral to LactMed for current data; radioactive compounds require temporary cessation.

How do clinicians decide whether a medication is safe?

The most reliable tool available is LactMed, the Drugs and Lactation Database maintained by the National Library of Medicine 4Ref 4National Institute of Child Health and Human Development / National Library of Medicine (2024).Drugs and Lactation Database (LactMed).LactMed as comprehensive, peer-reviewed, free, publicly accessible database of medication safety in lactation covering 1,500+ substances. It covers more than 1,500 substances, draws only from peer-reviewed literature, is continuously updated, and is available free at no cost. For each drug, LactMed provides: concentrations documented in breast milk, any observed effects in nursing infants, and alternative medications when concerns exist.

The 2022 *American Family Physician* clinical review by Spencer et al. recommends LactMed as "a convenient, government-sponsored, authoritative resource" and notes that prescribing decisions should favor medications with low oral bioavailability in the infant, high protein binding in the mother, and short half-lives 2Ref 2Spencer JP, Thomas S, Trondsen Pawlowski RH (2022).Medication Safety in Breastfeeding.RID <10% threshold; timing doses after feeding to minimize exposure; LactMed as authoritative free resource; sertraline as preferred SSRI with low RID; characteristics of safer medications (low oral bioavailability, high protein binding). Timing doses right after a feeding — so that peak maternal blood levels occur during the interval before the next feed — is a practical strategy to reduce infant exposure for medications with short half-lives 2Ref 2Spencer JP, Thomas S, Trondsen Pawlowski RH (2022).Medication Safety in Breastfeeding.RID <10% threshold; timing doses after feeding to minimize exposure; LactMed as authoritative free resource; sertraline as preferred SSRI with low RID; characteristics of safer medications (low oral bioavailability, high protein binding).

Your pharmacist, particularly a hospital or clinical pharmacist, can quickly look up any medication and apply these criteria. Your obstetrician, midwife, or primary care clinician are equally appropriate contacts. What you should not rely on is the medication's package insert: manufacturers routinely write "avoid during breastfeeding" for legal reasons even when the actual evidence for that drug is reassuring 3Ref 3Sachs HC; Committee on Drugs (AAP) (2013).The transfer of drugs and therapeutics into human breast milk: an update on selected topics.Only a small proportion of medications are contraindicated during breastfeeding; many mothers receive unnecessarily restrictive advice; codeine contraindication; referral to LactMed for current data; radioactive compounds require temporary cessation.

Which medication categories generally need closer review?

As a general orientation — not a substitute for checking your specific drug — the following categories have a broadly reassuring safety profile during breastfeeding 2Ref 2Spencer JP, Thomas S, Trondsen Pawlowski RH (2022).Medication Safety in Breastfeeding.RID <10% threshold; timing doses after feeding to minimize exposure; LactMed as authoritative free resource; sertraline as preferred SSRI with low RID; characteristics of safer medications (low oral bioavailability, high protein binding)3Ref 3Sachs HC; Committee on Drugs (AAP) (2013).The transfer of drugs and therapeutics into human breast milk: an update on selected topics.Only a small proportion of medications are contraindicated during breastfeeding; many mothers receive unnecessarily restrictive advice; codeine contraindication; referral to LactMed for current data; radioactive compounds require temporary cessation:

• Most common antibiotics (penicillins, cephalosporins, azithromycin)
• Acetaminophen (paracetamol) at standard doses
• Ibuprofen
• Several antidepressants — particularly sertraline, which has one of the lowest RIDs among the SSRIs, with infant serum levels often undetectable 2Ref 2Spencer JP, Thomas S, Trondsen Pawlowski RH (2022).Medication Safety in Breastfeeding.RID <10% threshold; timing doses after feeding to minimize exposure; LactMed as authoritative free resource; sertraline as preferred SSRI with low RID; characteristics of safer medications (low oral bioavailability, high protein binding)
• Most antihistamines (though sedating antihistamines warrant monitoring for infant drowsiness)

Categories that generally require individualized evaluation or closer monitoring include 2Ref 2Spencer JP, Thomas S, Trondsen Pawlowski RH (2022).Medication Safety in Breastfeeding.RID <10% threshold; timing doses after feeding to minimize exposure; LactMed as authoritative free resource; sertraline as preferred SSRI with low RID; characteristics of safer medications (low oral bioavailability, high protein binding)3Ref 3Sachs HC; Committee on Drugs (AAP) (2013).The transfer of drugs and therapeutics into human breast milk: an update on selected topics.Only a small proportion of medications are contraindicated during breastfeeding; many mothers receive unnecessarily restrictive advice; codeine contraindication; referral to LactMed for current data; radioactive compounds require temporary cessation:

• Opioid analgesics: Codeine is specifically contraindicated because ultra-rapid metabolizers can produce high levels of active morphine in milk, potentially causing infant respiratory depression. If an opioid is necessary, hydrocodone or low-dose morphine with short-duration use is generally preferred over codeine 3Ref 3Sachs HC; Committee on Drugs (AAP) (2013).The transfer of drugs and therapeutics into human breast milk: an update on selected topics.Only a small proportion of medications are contraindicated during breastfeeding; many mothers receive unnecessarily restrictive advice; codeine contraindication; referral to LactMed for current data; radioactive compounds require temporary cessation.
• Chemotherapy agents: Generally incompatible with breastfeeding.
• Radioactive compounds (used in some imaging studies): Typically require a defined period of pumping and discarding.
• Certain mood stabilizers: Require individual review — the evidence varies considerably by agent.
• Thyroid medications: Monitoring is often recommended; most doses used for hypothyroidism transfer minimally.

This is a rough orientation only. The specific agent, dose, your baby's age, and your baby's health all affect the picture.

What about antidepressants and mental health medications?

This is one of the most common areas of concern, and one of the most important to address thoughtfully. Untreated postpartum depression carries genuine risks — for both the parent and the baby, including effects on infant cognitive development, behavioral regulation, and the quality of the feeding relationship itself 5Ref 5American College of Obstetricians and Gynecologists (2023).Screening and Diagnosis of Mental Health Conditions During Pregnancy and Postpartum: ACOG Clinical Practice Guideline No. 4.Risks of untreated postpartum depression to parent and infant; importance of continuing effective mental health treatment postpartum.

The 2022 AAP policy statement on breastfeeding, by Meek and Noble, affirms that breastfeeding provides significant health benefits and that the decision to use medication compatible with breastfeeding should account for the full risk-benefit picture, including the risks of untreated illness 6Ref 6Meek JY, Noble L; Section on Breastfeeding (AAP) (2022).Policy Statement: Breastfeeding and the Use of Human Milk.AAP recommendation that breastfeeding's documented benefits make risk-benefit assessment essential when weighing medication decisions; breastfeeding as a public health imperative.

For depression, sertraline is the most extensively studied SSRI in lactation and consistently shows very low RID values — infant serum levels are typically undetectable or negligible 2Ref 2Spencer JP, Thomas S, Trondsen Pawlowski RH (2022).Medication Safety in Breastfeeding.RID <10% threshold; timing doses after feeding to minimize exposure; LactMed as authoritative free resource; sertraline as preferred SSRI with low RID; characteristics of safer medications (low oral bioavailability, high protein binding). Other SSRIs have broader evidence as well. The 2013 AAP clinical report by Sachs and the Committee on Drugs concluded that "only a small proportion of medications are contraindicated in breastfeeding mothers," and that many mothers receive unnecessarily restrictive advice 3Ref 3Sachs HC; Committee on Drugs (AAP) (2013).The transfer of drugs and therapeutics into human breast milk: an update on selected topics.Only a small proportion of medications are contraindicated during breastfeeding; many mothers receive unnecessarily restrictive advice; codeine contraindication; referral to LactMed for current data; radioactive compounds require temporary cessation.

If you are taking a medication for depression, epilepsy, thyroid disease, bipolar disorder, or any other serious condition: do not stop it without speaking to your clinician first. The risk of abrupt discontinuation may outweigh the risk of the medication itself.

What is 'pump and dump' and when does it actually apply?

Pumping and discarding milk (often called "pump and dump") does not accelerate drug clearance from your body or milk for most medications 2Ref 2Spencer JP, Thomas S, Trondsen Pawlowski RH (2022).Medication Safety in Breastfeeding.RID <10% threshold; timing doses after feeding to minimize exposure; LactMed as authoritative free resource; sertraline as preferred SSRI with low RID; characteristics of safer medications (low oral bioavailability, high protein binding). Drug levels in milk decline in parallel with drug levels in your bloodstream — time, not pumping, is what reduces exposure. Pumping without discarding, however, is useful to maintain milk supply when breastfeeding must be temporarily paused.

Pumping and discarding is genuinely indicated for a narrow set of situations: radioactive imaging agents (where a defined wait period is required), certain chemotherapy agents, and a small number of other substances with specific safety profiles. Your clinician can advise whether it applies to your situation.

The more broadly useful strategy for most medications is timing: taking a dose immediately after a feeding so that peak drug levels in milk occur during the longest interval before the next feed 2Ref 2Spencer JP, Thomas S, Trondsen Pawlowski RH (2022).Medication Safety in Breastfeeding.RID <10% threshold; timing doses after feeding to minimize exposure; LactMed as authoritative free resource; sertraline as preferred SSRI with low RID; characteristics of safer medications (low oral bioavailability, high protein binding).

What about your baby's age and health?

Your baby's ability to process any drug exposure through milk changes significantly with age. Newborns — especially those born preterm — have immature liver enzymes and kidney function, so they clear drugs much more slowly than older infants 1Ref 1Verstegen RHJ, Anderson PO, Ito S (2022).Infant drug exposure via breast milk.Pharmacokinetic factors determining drug transfer into breast milk; RID concept; clinical significance of low-level exposure; immature infant drug clearance in newborns3Ref 3Sachs HC; Committee on Drugs (AAP) (2013).The transfer of drugs and therapeutics into human breast milk: an update on selected topics.Only a small proportion of medications are contraindicated during breastfeeding; many mothers receive unnecessarily restrictive advice; codeine contraindication; referral to LactMed for current data; radioactive compounds require temporary cessation. A medication considered acceptably low-risk for a 4-month-old may warrant more caution in the first two weeks of life.

A baby who receives both breast milk and formula has proportionally lower exposure to any drug in milk. Babies with known liver or kidney conditions require special consideration. Always mention your baby's gestational age, birth history, and any health conditions when a clinician reviews a medication question.

By 6 months, most infants' hepatic clearance has matured substantially 1Ref 1Verstegen RHJ, Anderson PO, Ito S (2022).Infant drug exposure via breast milk.Pharmacokinetic factors determining drug transfer into breast milk; RID concept; clinical significance of low-level exposure; immature infant drug clearance in newborns, and the risk calculation for milk-transferred drugs generally becomes more favorable.

Do not let uncertainty lead to undertreated illness

One of the most consistent clinical messages in lactation pharmacology is this: stopping a necessary medication without guidance — or avoiding it altogether — is not automatically the safer choice 2Ref 2Spencer JP, Thomas S, Trondsen Pawlowski RH (2022).Medication Safety in Breastfeeding.RID <10% threshold; timing doses after feeding to minimize exposure; LactMed as authoritative free resource; sertraline as preferred SSRI with low RID; characteristics of safer medications (low oral bioavailability, high protein binding)3Ref 3Sachs HC; Committee on Drugs (AAP) (2013).The transfer of drugs and therapeutics into human breast milk: an update on selected topics.Only a small proportion of medications are contraindicated during breastfeeding; many mothers receive unnecessarily restrictive advice; codeine contraindication; referral to LactMed for current data; radioactive compounds require temporary cessation6Ref 6Meek JY, Noble L; Section on Breastfeeding (AAP) (2022).Policy Statement: Breastfeeding and the Use of Human Milk.AAP recommendation that breastfeeding's documented benefits make risk-benefit assessment essential when weighing medication decisions; breastfeeding as a public health imperative. Untreated or poorly controlled illness in a breastfeeding parent carries real risks, sometimes greater than the medication's risk.

In most cases, the question is not "medication or breastfeeding" but rather "which medication, at what dose, with what monitoring" — and with proper guidance, the answer is almost always that both can continue. Research consistently shows that many breastfeeding parents receive unnecessarily restrictive advice that leads to premature weaning 1Ref 1Verstegen RHJ, Anderson PO, Ito S (2022).Infant drug exposure via breast milk.Pharmacokinetic factors determining drug transfer into breast milk; RID concept; clinical significance of low-level exposure; immature infant drug clearance in newborns3Ref 3Sachs HC; Committee on Drugs (AAP) (2013).The transfer of drugs and therapeutics into human breast milk: an update on selected topics.Only a small proportion of medications are contraindicated during breastfeeding; many mothers receive unnecessarily restrictive advice; codeine contraindication; referral to LactMed for current data; radioactive compounds require temporary cessation, a genuinely harmful outcome given the documented benefits of continued breastfeeding.