Use of marijuana in early pregnancy can harm the foetus and cause developmental delays and learning disabilities in babies scientists have warned.

The study at Georgetown University Medical Centre in the US suggests an urgent need for human epidemiological and basic research that examines the link between maternal cannabinoid use either smoked or eaten in candy bars and the health of newborns.

Cannabinoids are chemicals like THC the primary psychoactive compound in marijuana that act on cannabinoid receptors in neurons repressing the normal release of neurotransmitters.

quot;We know from limited human studies that use of marijuana in early pregnancy is associated with many of the same risks as tobacco including miscarriage birth defects developmental delays and learning disabilities but animal research suggests the potential for many more developmental issues linked with the drugquot; said G Ian Gallicano associate professor at Georgetown.

Gallicano said one reason for limited research is that the classification of marijuana as a Schedule I drug creates challenges to conducting research.

quot;All of the model systems point to the notion that cannabinoids affects many aspects of human development because THC and other chemicals alter molecular pathways that shouldn’t be disrupted during development of a foetusquot; he said.

quot;We also know that THC is a promising agent for treating cancer because it negatively affects tumour growth and can cause the death of cancer cellsquot; he added.

quot;Embryo development has similarities to tumour formation – it turns on growth pathways that are necessary for developmentquot; Gallicano said.

quot;The fact that THC seems to stop cancer growth suggests how damaging the chemical could be for a foetusquot; he added.

Researchers reviewed the scientific literature for studies on cannabinoids and embryonic development published between 1975 and 2015.

They found that THC lasts in the body for weeks especially in maternal tissues that act as reservoirs for THC and other cannabinoids according to studies of pregnant dogs.

Human cells studies have shown that THC has a half-life of eight days in fat deposits and can be detected in blood for up to 30 days they said.

Another study showed that THC readily crosses the human placenta which can slow clearance of the drugs while prolonging foetal exposure.

THC levels in smoked marijuana have increased nearly 25-fold since 1970 and can be substantially stronger in edible preparations of cannabis researchers found.

THC and other cannabinoids interfere with use of folic acid vitamin B9 which has long been known to be essential for normal development and growth of the human placenta and embryo.

Deficiencies in folic acid are linked to low human birth weight increased risk of spontaneous abortion and neural tube defects.

Cannabinoid signalling plays important roles in development of a mouse embryo. It is required for proper pre-implantation development embryo transport to the uterus and implantation.

The research was published in the journal BioMed Central BMC Pharmacology and Toxicology.

nbsp;