Belfast - Women risk losing their babies if they smoke cannabis at the time of conception or early in pregnancy, a study suggests.
Researchers working with mice found that THC, the psychoactive ingredient in the drug, can prevent an embryo reaching the womb.
The findings suggest that smoking cannabis may lead to miscarriages or ectopic pregnancies, caused by embryos developing outside the womb in the Fallopian tube.
Writing in the Journal of Clinical Investigation, the United States researchers, led by Dr Sudhansu Dey from Vanderbilt University in Nashville, Tennessee, warned: "Our observation of defects of pre-implantation events and pregnancy failure in mice exposed to excessive THC raises concern that the adverse effects of maternal use of marijuana could be seeded very early in pregnancy."
THC, or tetrahydrocannabinol, binds to two receptors in the brain called CB1 and CB2.
Receptors are proteins into which other molecules fit like a key in a lock. Biological processes are triggered when molecules bind on to receptors.
THC activity in the brain leads to the "high" enjoyed by cannabis users. But CB receptors are also found in the sperm, eggs and newly formed embryos.
During early pregnancy, a naturally occurring signalling molecule called anandamide normally activates these receptors. The scientists found that anandamide levels are carefully balanced to maintain normal embryonic development.
If anandamine was allowed to be too active, embryos were prevented from completing their passage to the uterus.
When pregnant female mice were exposed to THC, the drug compound had the same effect on the CB1 receptor as anan-damine. The effect of THC persisted and "swamped" the finely tuned signalling system.
Embryos recovered from the treated mice also showed signs of apoptosis - the natural process by which defective cells destroy themselves. - Belfast Telegraph