Drugs in Lactation Definitions

Sarah Fenner, Acting Co-Director, Midlands and East Medicines Advice Service (Midlands site) & UK Drugs in Lactation Advisory ServicePublished

Risk classification

The compatibility of drugs with breastfeeding has been assessed through a combination of risk to the breastfed infant and the quality/volume of evidence available. Drugs have been assigned to one of three categories which are defined as:


  • Serious adverse effects have been reported, or are considered possible, in a breastfed infant.
  • Lactation could be compromised because of an impact on milk production.


  • Minor and/or reversible adverse effects have been reported, or are considered possible, in breastfed infants, but which are not considered to pose an unacceptable risk to the infant.
  • Insufficient evidence of the amount of drug excreted into breast milk.
  • Insufficient evidence, or experience of use in practice, to guarantee safe use with breastfeeding.
  • Use of a medicine is conditional on risk-reducing actions being taken, e.g monitoring the infant, delaying breastfeeding after a maternal dose, using a lower-risk formulation etc.


  • Levels in milk are sufficiently low, or predicted to be low because of the drug’s properties, that they would not present an appreciable risk to the infant..
  • Substantial clinical experience of the drug has not indicated any risks.
  • The medicine is in clinical use in young infants at doses significantly exceeding those which would be ingested through breast milk.

Seek Advice

  • Use of this drug requires an assessment of potentially complex issues, including an assessment of risk and safety in individual cases.
  • For example, the drug may normally be used in combination with other drugs which may present additional risks to those posed by the drug alone. This would apply to the treatment of HIV infection or cancer in breastfeeding mothers, although other therapy areas may also fit these criteria.