U.S. scientists say they don't believe the theory that experimentation with marijuana is harmless and won't lead to further drug use.
Researchers at the Mount Sinai School of Medicine in New York note that, or cannabis, is often called a "gateway drug," suggesting addiction to one drug could make a person vulnerable to abuse and addiction of harder drugs.
The most common argument against the gateway drug theory is that adolescents move to harder drugs because of peer or emotional pressures. But now Professor Yasmin Hurd and colleagues say they've demonstrate in animal models that cannabis can affect future sensitivity to heroin.
Studying neurobiological events after cannabis exposure, they found marijuana affects the human brain's natural chemicals called endogenous opioids, which are known to play a role in heightening positive emotions, and creating a sense of reward. That's the same system stimulated by hard drugs.
The team's results dispel the common belief that drug experimentation doesn't affect the brain and demonstrates the brain may "remember" previous usage and make users vulnerable to harder drugs later in life.
The research appears in the online edition of the journal Neuropsychopharmacology.
Copyright 2006 by United Press International
Explore further: Study explains why hemp and marijuana are different