Anticoagulants and Breastfeeding

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The information provided is taken from various reference sources.  It is provided as a guideline.  No responsibility can be taken by the author or the Breastfeeding Network for the way in which the information is used.  Clinical decisions remain the responsibility of medical and breastfeeding practitioners.  The data presented here is intended to provide some immediate information but cannot replace input from professionals.

Breastfeeding mothers can feed as normal following use of heparin, warfarin and low molecular weight heparinoids.

Blood clots may develop in the calves (deep vein thrombosis/DVT) or the lungs (pulmonary embolism/PE).  Risks increase in patients who smoke or who are overweight.  They increase if the person is immobile for prolonged periods e.g. during travel or after surgery.  Anti-coagulants are used frequently to prevent the development of DVT in those at risk.  For further information see

Pregnancy increases your chances of getting DVT, with approximately 1 in 1,000 pregnant women developing the condition.  The risk is considerably increased if your Body Mass Index (BMI) is over 30 (NICE 2010). 

The symptoms of a DVT in the leg include:

  • swelling,
  • pain,
  • warm skin,
  • tenderness, and
  • redness, particularly at the back of your leg, below the knee.

A DVT usually (although not always) affects one leg (NHS Choices

If you have a BMI of more than 30, have a previous history of DVT or develop symptoms of a DVT or PE you may be given daily injections of heparin or a low molecular weight heparinoid (enoxaparin, dalteparin or tinzaparin ) (BNF).  

These drugs do not pass into breastmilk in any significant amount as the molecules are very large and the drugs have very poor oral bioavailability (Hale. Jones, LactMed).

Enoxaparin was studied by Guillonneau (1996) in 12 women receiving 10-20 milligrammes: after 57 days of exclusive breastfeeding their infants showed no change in anticoagulant activity or evidence of bleeding.

Although there are no studies on transfer of tinzaparin into breastmilk, there is no reason to suggest that it will pass through to the baby due to its lack of oral bioavailability (Hale. Jones, LactMed).

In another study (Richter 2001) of 15 patients who had undergone caesarian section, breastmilk levels of dalteparin measured were less than 0.037 international units (IU) per millilitre and no adverse events were reported.

Alternatively women may be prescribed warfarin tablets to take.  Warfarin is an anticoagulant that is taken as tablets once daily (NICE 2010).  The dose of warfarin has to be precise to ensure that the blood does not clot too easily, or that it does not cause excessive bleeding.  This may involve regular monitoring of INR (a measure of clotting levels) by blood tests.

Mothers can continue to breastfeed normally whilst taking warfarin up to 12milligrammes daily, as levels passing through breastmilk are too low to affect your baby’s blood clotting (Orme 1977).  No adverse reactions in breastfed infants have been reported from maternal warfarin use during lactation.


  • British National Formulary
  • Guillonneau M, de Crepy A, Aufrant C, Hurtaud-Roux MF, Jacqz-Aigrain E.L’allaitement est possible en cas de traitment maternal par l’enoxaprine. Arch Pediatr (Paris). 1996;4:513-4
  • Hale T. W Medications in Mothers Milk
  • Jones W Breastfeeding and Medication 2018 Routledge
  • Lactmed website
  • NICE Guidance. Reducing the risk of venous thromboembolism (deep vein thrombosis and pulmonary embolism) in patients admitted to hospital
  • Orme ML, Lewis PJ, de Swiet M, Serlin MJ, Sibeon R, Baty JD, Breckenridge AM. May mothers given warfarin breastfeed their infants? BMJ 1977; 1: 1564–58. Orme ML, Lewis PJ, de Swiet M, Serlin MJ, Sibeon R, Baty JD, Breckenridge AM. May mothers given warfarin breastfeed their infants? BMJ 1977; 1: 1564–5
  • Richter C, Sitzmann J, Lang P, Weitzel H, Huch A, Huch R.Excretion of low molecular weight heparin in human milk. Br J Clin Pharmacol. 2001;52:708-10

© Dr Wendy Jones MBE, MRPharmS and the Breastfeeding Network Sept 2019