Researchers claim that those who use marijuana on a regular basis during their teenage and early adult years may be using it as a 'gateway drug', which may create a craving for the chemical stimulation of harder drugs.
They also add that the effect on chemicals called endogenous opiods may leave a memory in the brain which makes the user vulnerable to harder drugs later in life.
According to the Daily Mail, the study, published by the journal Neuropsychopharmacology, looked at the behavior of young rats exposed to cannabis.
The rats took in much larger doses of opium when trained to self administer than other rodents.
Dr Yasmin Hurd of the Mount Sinai School of Medicine, New York, said cannabis affects some of the brain's natural chemicals that heighten a person's emotions, which also works with hard drugs, meaning to brain may remember previous usage.
Earlier claims believed adolescents who move on to hard drugs do so because of peer pressure or environmental or emotional issues that would have made them vulnerable without exposure to cannabis.
