Red flags — call us immediately or go to the Emergency Department if:
- Is much more sleepy than usual, floppy, or cannot be woken
- Is not feeding, or feeding much less than usual
- Seems limp, with little muscle tone
- Has slow or irregular breathing, or turns blue around the lips
- Has a very slow heart rate (beats seem far apart when you hold the baby)
- Has a seizure or jerky movements
- Temperature is very low (below 36.5 °C) or high (≥38 °C)
- Seems very pale, grey, or mottled
- A rash that does NOT fade when you press a clear glass on it — sepsis sign
- Fever in a baby under 3 months (any temperature ≥ 38.0 °C)
- Fast breathing, blue lips, or sucking-in of the ribs — breathing emergency
What the research shows
THC — the main active compound in cannabis — passes into breast milk. Studies show that THC concentrates in breast milk at levels up to 8 times higher than in the mother's blood. It stays in milk for at least 6 days after a single use. In mothers who use cannabis regularly, THC can be found in milk for weeks. The baby takes in THC with each feed.
What this means for the baby
Young babies cannot break down THC well. In breastfed babies exposed to THC through milk, researchers have found slower motor development, impaired early childhood brain development, and poorer scores on tests of thinking and behaviour at school age. In rare cases, high doses — for example from cannabis extracts or edibles — can cause serious sedation in the baby.
The recommendation — and we understand it is not always easy
All major medical organisations — including the WHO, the Academy of Breastfeeding Medicine, and Belgian health authorities — advise against cannabis use while breastfeeding. There is currently no proven safe level. If you use cannabis for a medical reason (pain, anxiety, insomnia), we can help you find safe alternatives that are compatible with breastfeeding. Please reach out — there is no judgement here.
If you have used cannabis and are breastfeeding
A single episode of use is different from daily use. If you have used cannabis once, do not stop breastfeeding abruptly — the benefits of breast milk are substantial and stopping suddenly has its own risks. Contact us to talk through options, including timing of feeds, temporary pumping, and support to reduce or stop use. We are here to help, not to judge.
Vitamin D for the baby
Regardless of this situation, every baby needs 400 IU (10 µg) of vitamin D a day from birth, breastfed or formula-fed. Continue through childhood; ask us how long. If you have not started it yet, ask your midwife or GP.
If anything changes
If your baby becomes very sleepy or floppy, stops feeding, has slow breathing, or you are worried — call 112 immediately.
Emergency? Call 112. Do not wait for a reply from us.
If you are not sure, ask
Send us what you are seeing. A few lines are enough to start.
An assistant takes your message. A coordinator reads it. A doctor decides.
Message us on WhatsAppReviewed and signed off by Dr Didier Decamps on 21 September 2026. This is general information and does not replace an individual assessment by a qualified clinician.
Written with AI assistance. Reviewed, corrected and signed by Dr Didier Decamps, paediatrician.
Last reviewed: 21 September 2026