Exposure to a cannabis in the womb could cause children to experience learning difficulties and hyperactivity, researchers suggest.
An extract of cannabis was used in the research
Research was carried out on rats using an artificial cannabinoid, a cannabis extract.
Cannabis is the most widely used drug by women at reproductive age.
Previous research has shown that babies born to mothers who took cannabis while they were pregnant go on to experience problems with physical activity.
In this latest study, researchers injected pregnant rats each day with a quantity of the cannabinoid equivalent to a low to moderate daily dose in humans.
Cannabinoids can be transferred from the mother to the offspring through the placental blood
They then compared the baby rats' development with that of a group of rats born to mothers who had not been given the cannabinoid.
The Italian research team said studies on rats could provide more conclusive results than human tests, where findings could be complicated by factors such as impure drugs and cigarette smoking.
Each group of rats were given tests to assess their memory and motor activity.
They were examined as infants (12-days-old), juvenile (40-days-old) and adult (80-days-old).
When the rats were young, those exposed to the cannabinoid were significantly more hyperactive than the other group, though this difference disappeared by adulthood.
But the cannabinoid rats scored lower on learning tests throughout their lives.
The researchers, from the University of Cagliari, Cittadella Universitaria di Monserrato, Italy, used an artificial cannabinoid called WIN in their study.
Post-mortem examinations of the rats brains were carried out.
They found that exposure to WIN in the womb disrupted the release of a neurotransmitter called glutamate which transmits nerve impulses between brain cells.
It also affected a process called long-term potentiation, electrical activity in the brain associated with learning and the formation of memory.
It is believed the effect on glutamate production led to the problems in forming memories in the hippocampus area of the brain.
Researcher Professor Vincenzo Cuomo told BBC News Online: "We cannot say the findings in rats can be directly translated to humans, but we know that animal studies can generate predictive information on various aspects of human brain function."
Brain receptors which trigger the behavioural effects of cannabis have been found to be present in rat brains during prenatal development.
Professor Cuomo added: "Cannabinoids can be transferred from the mother to the offspring through the placental blood during the gestation both in humans and in rodents.
"In addition, as for tobacco smokers, a daily use of marijuana exposes the foetus to carcinogens produced by burning marijuana and carbon monoxide which has been shown to affect the health of the foetus."
Writing in the journal Proceedings of the National Academy of Science, the researchers said the findings were in line with previous studies indicating cannabis taken during pregnancy affected the cognitive development of the unborn child, particularly memory.
They added: "Moreover, the increased motor activity observed in both infant and juvenile offspring of WIN-treated dams [mother rats] is consistent with data showing that children prenatally exposed to marijuana were rated, at a puberty age, as hyperactive, inattentive, and particularly impulsive."
Roger Howard, chief executive of the charity DrugScope, said: "There is little correlation between the brain patterns of rats and humans and I would therefore be cautious about placing too much emphasis on a single piece of research."
His comments were echoed by John Witton, of the charity Action on Addiction.
He said: "Previous studies have shown that children who have been exposed to cannabis in the womb have poor attention, memory and cognitive functioning.
"However, these effects are small compared to those from tobacco.
"Cannabis exposure may be to blame, but a child's development may also be affected by the reasons underlying some mothers' choice to use cannabis during pregnancy."