Pot may indeed lead to heroin use, rat study shows

NEW YORK, July 13 (Reuters) Teens who experiment with marijuana may be making themselves more vulnerable to heroin addiction later in life, if the findings from experiments with rats are any indication.

''Cannabis has very long-term, enduring effects on the brain,'' Dr Yasmin Hurd of the Mount Sinai School of Medicine in New York, the study's lead author, told Reuters Health in an interview.

Whether or not trying marijuana is a 'gateway' to use of so-called harder drugs like heroin and cocaine has been hotly debated, she and her colleagues note in the journal Neuropsychopharmacology.

To investigate whether pot smoking could cause brain changes that might predispose an individual to later drug use, 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 were more sensitive to the effects of heroin, the researchers found, and also consistently used 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 said.

She and her colleagues conclude: ''The current findings provide direct evidence in support of the gateway hypothesis that adolescent cannabis exposure contributes to greater heroin intake in adulthood.'' REUTERS MQA RN1044