Chan 2004: naltrexone in breast milk, measured in one mother

What they tested

Researchers took repeated milk and blood samples from one 30-year-old breastfeeding mother being treated with oral naltrexone for opioid addiction. Sampling covered 19.3 hours of a dosing interval once the drug had reached steady levels in her body.

They measured naltrexone and its main breakdown product, 6,beta-naltrexol, and used the results to estimate how much the baby took in, compared with the mother's dose adjusted for body weight. They also tested the baby's blood.

What they found

The estimated infant dose relative to the mother's weight-adjusted dose was 0.03% for naltrexone and 0.83% for 6,beta-naltrexol, counted as naltrexone equivalents. Over the full 24-hour dose interval, the total was estimated at 1.06%.

Only 6,beta-naltrexol was found in the baby's blood, at a very low level of 1.1 micrograms per litre. Naltrexone itself was not detected.

The 6-week-old baby was healthy, reaching expected milestones, with no adverse effects. The authors said naltrexone should be used during breastfeeding only after weighing the risks and benefits for each person.

Limits

• It's a report on one mother and one baby, so it can't show how much other babies would take in or whether rare effects occur.
• The baby was checked at 6 weeks old, which says nothing about longer-term effects.
• The mother was taking oral tablets, so the results don't apply directly to the monthly shot.

What it means if you're considering naltrexone

For someone breastfeeding and considering naltrexone, this is one of only two published measurements in breastfed babies that the site found. It suggests the amount reaching the baby through milk is small and that this baby did well, but one case is a thin basis for a decision. The authors' own advice is to weigh the risks and benefits individually, which is a conversation to have with a prescriber.