Cannabis and Pregnancy — Why Consumption Is Off Limits

## A Clear Message

In the cannabis debate there are areas where nuance is appropriate – and areas where clarity is essential. Cannabis during pregnancy and breastfeeding belongs to the second category. All relevant medical professional bodies – the German Society for Gynaecology and Obstetrics, the American College of Obstetricians and Gynecologists, the WHO – agree: cannabis use during pregnancy and breastfeeding carries significant risks for the unborn or newborn child and should be avoided entirely.

## How THC Crosses the Placenta

THC is a highly lipophilic (fat-soluble) substance with a low molecular weight. These properties allow the molecule to cross the placental barrier virtually unimpeded. Studies show that foetal blood reaches THC concentrations of approximately one-third to one-half of the maternal plasma concentration. This means: when a pregnant person consumes cannabis, the foetus is also exposed to the substance.

The endocannabinoid system plays a central role in embryonic and foetal development. CB1 and CB2 receptors are already detectable in the developing brain during the first weeks of pregnancy. The endogenous cannabinoid system regulates critical processes such as neuronal migration, synaptogenesis and the formation of neural circuits. Exogenous THC can disrupt these finely tuned processes.

## Risks for Foetal Development

The scientific evidence on the effects of cannabis on pregnancy encompasses several well-documented risk areas:

Birth weight and preterm birth: Several meta-analyses, including a comprehensive evaluation by the University of Ottawa from 2016 involving over 24,000 pregnancies, show a significant association between cannabis use during pregnancy and lower birth weight. The risk of preterm birth is also elevated.

Neurological development: The OPPS study (Ottawa Prenatal Prospective Study) and the MHPCD study (Maternal Health Practices and Child Development) have followed children whose mothers consumed cannabis during pregnancy since the 1980s. The results show abnormalities in attention, working memory, impulse control and executive functions – deficits that were detectable into adolescence.

Placental complications: There is evidence that cannabis use may increase the risk of placental abruption – a potentially life-threatening complication.

Behavioural abnormalities: Children with prenatal cannabis exposure show behavioural abnormalities more frequently in long-term studies, including increased hyperactivity and difficulties in social interactions.

## Breastfeeding: THC in Breast Milk

Due to its fat solubility, THC accumulates in breast milk. Studies show that THC can be detectable in breast milk for up to six days after the last use. There is no safe interval between consumption and breastfeeding that would eliminate the risk. CBD products are also not recommended during breastfeeding, as the data on their safety is insufficient.

## No Safe Dose

A common misconception is the assumption that occasional or low-level use is harmless. Current research cannot define a threshold dose below which cannabis is considered safe during pregnancy. The recommended dose is therefore zero. This applies regardless of the method of consumption – smoking, vaporising, edibles and topical applications containing THC are all to be avoided equally.

## What to Do If Currently Using?

Pregnant individuals who currently use cannabis should disclose this to their attending physician or midwife. There are no criminal consequences for this openness, and only with this information can medical care be optimally adjusted. For cannabis-dependent pregnant individuals, abrupt cessation can in rare cases be problematic – in such cases the approach should be medically supervised.

Counselling services such as the BZgA telephone helpline (0800 135 3771) and local addiction counselling centres offer confidential support.