Cannabis, pregnancy and breastfeeding: the facts

TL;DR

• THC crosses the placenta – foetal concentration reaches ~10-30 % of maternal levels.
• Associated with lower birth weight (-100-200 g), preterm birth and cognitive differences (Metz 2022).
• THC accumulates in breast milk, detectable up to 6 days.
• Clear guidance from FOPH, SSGO and WHO: no cannabis in pregnancy or breastfeeding.

What THC does to the foetus

THC binds CB1 receptors in the developing brain and disrupts neuronal migration and synaptic maturation. Long-term follow-up shows more impulsivity and less attention at school age.

Breastfeeding: why caution continues

THC is lipophilic and accumulates in breast milk. Even occasional use can expose infants to meaningful doses – motor development effects have been reported.

Pharmacokinetics and the foetal barrier

The unique chemical properties of tetrahydrocannabinol facilitate its passage across the placental barrier. As a highly lipophilic substance, THC dissolves easily in lipids and penetrates the cellular barriers of the placenta without significant resistance. In the foetal organism, the active substance is preferentially distributed in structures rich in adipose tissue, which include in particular the developing nervous system and the brain. Since the foetal blood-brain barrier is not yet fully mature, the unborn life is directly exposed to circulating cannabinoids.

The breakdown of these substances poses significant physiological challenges for the foetal organism. The enzymes responsible for metabolism in the foetal liver are present with only minimal activity compared to adults. This leads to a highly delayed excretion and a prolonged half-life of the active substances in the foetal bloodstream. Even after the maternal active substance level has dropped, the cannabinoids and their metabolites remain in the foetal tissue for a longer period and can continuously influence biological processes there.

• High lipophilicity facilitates passage through the placental barrier
• Accumulation in the lipid-rich tissue of the fetal brain
• Immature fetal liver enzymes delay the breakdown of cannabinoids
• Prolonged residence time of the active substances in the fetal bloodstream

Swiss advisory practice and legal framework

In Swiss healthcare practice, gynecologists, midwives, and pediatric specialists play a central role in patient education. The official guidelines of the Federal Office of Public Health (FOPH) and the Swiss Society of Gynecology and Obstetrics (SGGG) serve as a binding reference for medical counseling. In cases of suspected regular consumption during pregnancy, Swiss hospitals aim for interdisciplinary care to minimize risks at an early stage. Counseling is confidential, but consistently aims for complete harm reduction and immediate cessation of use.

Legally, the consumption of THC-containing cannabis with a total THC content of over one percent is generally prohibited in Switzerland. For pregnant women, the same strict zero-tolerance limit of 1.5 micrograms of THC per liter of blood applies in road traffic, exceeding which leads to immediate unfitness to drive. In severe cases of substance use that could endanger the child's welfare after birth, medical professionals are obliged, in compliance with legal requirements, to cooperate with the competent child protection authorities to ensure the well-being of the newborn.

• Guidelines of the FOPH and SGGG as the basis of medical education
• Interdisciplinary care in Swiss maternity hospitals in cases of consumption
• Applicability of the 1.5 microgram THC limit in road traffic
• Legal protective measures in cases of endangerment of child welfare

Evidence-based alternatives for pregnancy complaints

Many pregnant women consider using cannabis to relieve typical symptoms such as morning sickness, sleep disorders, or anxiety. However, as the data on the risks of cannabinoids clearly advises against use, safe, evidence-based alternatives must take priority. For mild to moderate nausea, non-pharmacological measures such as acupressure, ginger preparations, or dietary adjustments have proven effective. These methods offer clinically proven efficacy without exposing the unborn child to the risks of psychoactive or incompletely researched substances.

In more severe cases, such as hyperemesis gravidarum, or in the case of pronounced sleep problems, those affected should under no circumstances resort to self-medication with cannabis or CBD. The Swiss Agency for Therapeutic Products, Swissmedic, approves specific medicines for these indications that have been tested during pregnancy and can be used safely under medical supervision. Close consultation with the treating physician or a pharmacy ensures that both the mother's health and the child's development are optimally protected and that therapeutic measures are evidence-based.

• Ginger preparations and acupressure as safe options for nausea
• Avoiding self-medication with CBD or THC for sleep disorders
• Use of Swissmedic-approved medicines under supervision
• Close coordination with Swiss specialists and pharmacies

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