Low molecular weight heparin and unfractionated heparin can be used during breastfeeding. Recommendations apply to full term, healthy infants only.

General considerations

It is important to complete an individual risk assessment for your patient and to apply the principles of prescribing in breastfeeding when looking at the available information and making treatment decisions.


Any heparin (low molecular weight (LMWH), or unfractionated) can be used during breastfeeding.

Negligible amounts are expected to pass into breast milk due to the large molecular weight and any drug present in the breast milk would not be expected to be absorbed by the breastfed infant.

Clinical considerations

The choice of heparin will depend on the clinical indication. Treatment choice should be based on the clinical scenario with safety in breastfeeding a secondary consideration.

Specific recommendations

Patient Information

The NHS website provides advice for patients on the use of specific medicines in breastfeeding.

Contact us

Get in touch with the UK Drugs In Lactation Advisory Service (UKDILAS), our specialist breastfeeding medicines advice service if you need support in the following situations:

  • you need further advice
  • the medicine in question is not included here
  • the infant is unwell or premature
  • multiple medicines are being taken

About our recommendations

Recommendations are based on published evidence where available. However, evidence is generally very poor and limited, and can require professional interpretation. Assessments are often based on reviewing case reports which can be conflicting and lack detail.

If there is no published clinical evidence, assessments are based on: pharmacodynamic and pharmacokinetic principles, extrapolation from similar drugs, risk assessment of normal clinical use, expert advice, and unpublished data. Simulated data are now increasingly being used due to the ethical difficulties around gathering good quality evidence in this area.


Full referencing is available on request.

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