http://www.dailymail.co.uk/health/article-395704/Cannabis-gateway-harder-drugs.htmlCannabis a 'gateway to harder drugs'Teenage pot smokers are much more likely to go on to use harder drugs, such as heroin, claims a new report.
Researchers insist they now have scientific proof that cannabis works as a gateway drug and makes young users more physically vulnerable to heroin addiction later in life.Drugs
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The landmark study is certain to have an impact on the debate over whether to legalise the so-called soft drug.
And it is a major boost for anti-drug campaigners who argue that peer pressure and exposure to dealers peddling marijuana tempts teens to escalate their drug use.
Published in the online scientific journal Neuropsychopharmacology, it claims using cannabis damages the developing brain chemistry in smokers aged under 21, making them more likely to become hooked on heroin.
"Cannabis has very long-term, enduring effects on the brain," said Dr.
Jasmin Hurd, of the Mount Sinai School of Medicine in New York, who led the study.
She said her findings provide direct evidence in support of the gateway hypothesis that adolescent cannabis exposure contributes to
greater heroin intake in adulthood.
Using young rats, Hurds team found those exposed to cannabis during adolescence took in much larger doses of heroin when the animals were trained to self-administer it.
The results challenge those who claim that drug experimentation does not affect the brain.
They showed that the brain may "remember" previous usage and subsequently crave a bigger fix of harder drugs.
The experiment using rats was set up to mirror human use as closely as possible.
Hurd and her team looked at rats exposed to the active ingredient in marijuana, THC, during a developmental period similar to human
adolescence. To mimic the relatively small amount used by most teens experimenting with pot, the rodents received periodic, small doses of THC.
As young adults, the animals were fitted with catheters that allowed them to self-administer heroin. The researchers compared the amount and
frequency of their drug use with that of rats that had not been given THC previously.
The THC-exposed rats consistently took larger amounts of the drug.
The researchers also found that the THC-exposed rats showed disturbances in the brain's endogenous opioid system, which is often
popularly referred to as the "reward system" of the brain and, in humans, is involved in experiencing pleasure.
"I was really surprised at how specific and enduring the effects of cannabis were," Hurd added.
Neurologist Jim van Os, a cannabis expert at the University of Maastricht in the Netherlands, said the findings show the drugs
damaging effects on the reward structures of the brain.
He added: There is now overwhelming evidence that nobody in the brains developmental stage under the age of 21 should use
cannabis.
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