Medications to Avoid in Breastfeeding (Lactating) Mothers

Absolutely Contraindicated - Breastfeeding Must Stop

These drugs require complete cessation of breastfeeding:

Drug/Category	Reason
Anticancer / cytotoxic drugs (e.g., methotrexate, cyclophosphamide)	Immunosuppression, mucosal damage, potential carcinogenicity in infant
Radioactive substances / radiopharmaceuticals	Radiation exposure to infant via milk
Amphetamines (including recreational stimulants)	CNS stimulation, poor feeding, growth issues in infant
Ergotamines	Vasospasm, ergotism in infant
Statins (e.g., atorvastatin, simvastatin)	Lipid metabolism disruption in the developing infant
Nitrofurantoin (in infants <1 month or with G6PD deficiency)	Hemolytic anemia risk

Tintinalli's Emergency Medicine, Table 99-7 (WHO General Cautions)
Rheumatology 2-Volume Set, Table 145.1

Avoid Unless Absolutely Necessary

Drug	Concern
Chloramphenicol	Bone marrow suppression ("gray baby syndrome")
Tetracyclines	Bone and teeth discoloration in infant
Fluoroquinolones (e.g., ciprofloxacin)	Potential cartilage toxicity in infant

Use with Caution - Monitor Infant

Watch for Drowsiness / CNS Depression

Phenobarbital and other anticonvulsants - sedation, poor feeding
Benzodiazepines - lethargy, weight loss, respiratory depression
Opioids (especially codeine - AVOID: converts to morphine rapidly in ultra-rapid metabolizers, cases of infant death reported)
Selected psychiatric drugs - tricyclic antidepressants, antipsychotics

Watch for Jaundice / Hemolysis

Sulfonamides - compete with bilirubin binding, risk of kernicterus
Dapsone - hemolysis
Mefloquine, sulfadoxine/pyrimethamine (Fansidar) - jaundice

Watch for Thyroid Effects in Infant

Propylthiouracil (PTU) and methimazole/carbimazole - can cause neonatal hypothyroidism (if used, monitor infant thyroid function)

May Suppress Milk Supply - Use an Alternative

Estrogens (including combined oral contraceptive pills) - reduce prolactin-driven milk production
Thiazide diuretics - reduce milk supply

Immunosuppressants in Rheumatic Disease (Summary)

Drug	Lactation Status
Azathioprine	Generally compatible (<1% transfer)
Hydroxychloroquine	Safe
Cyclosporine	Safe (minimal transfer)
Methotrexate	Avoid (recommend avoiding despite minimal transfer)
Leflunomide	Avoid (insufficient safety evidence)
Mycophenolate mofetil (MMF)	Avoid (insufficient safety evidence)
Cyclophosphamide	Avoid (ACR/EU guidelines)

Rheumatology 2-Volume Set, Table 145.1

Psychotropic Drugs

Lithium - passes into breast milk significantly; risk of toxicity in infant (lethargy, cyanosis, hypotonia); generally avoid or use with very close monitoring
Clozapine - contraindicated during breastfeeding (agranulocytosis risk)
SSRIs - most (sertraline, paroxetine) are considered relatively safe; fluoxetine has the highest milk transfer and should be used cautiously
No psychotropic drug is entirely without risk - individual benefit/risk assessment is required

Key Principles for Safe Prescribing in Lactation

Check each drug individually - use resources like LactMed (NIH) for the most current data
Timing matters - taking medication immediately after breastfeeding (or before the infant's longest sleep period) reduces infant exposure
Milk-to-plasma ratio - drugs with low protein binding, low molecular weight, and high lipid solubility transfer more readily into breast milk
Relative infant dose (RID) - an RID <10% is generally considered acceptable
Premature or jaundiced infants are more vulnerable and require stricter precautions

Always weigh the benefit of breastfeeding (which is substantial) against the risk of drug transfer. Many conditions can be managed with safer alternatives that allow continued breastfeeding.

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