Young people who smoke cannabis are more likely to get hooked on cigarettes in later life
Exposure to THC, main psychoactive ingredient in marijuana, can increase addictive properties of nicotineCigarettes often considered a 'gateway' to other drugs, but this shows the reverse can be true
14:31 GMT, 11 January 2013
14:52 GMT, 11 January 2013
Exposure to THC, the main psychoactive ingredient in marijuana, can increase the addictive properties of nicotine
Young people who smoke cannabis are also more likely to become addicted to cigarettes – increasing their risk of heart disease and lung cancer.
Exposure to THC (tetrahydrocannabinol), the main psychoactive ingredient in marijuana, can increase the addictive properties of nicotine, a study shows.
The research, published online in the journal Neuropsychopharmacology, suggests previous cannabis use may make people more vulnerable to nicotine dependence and tobacco related diseases.
Cigarettes are often considered a 'gateway' to other drugs, but there is now evidence to show the reverse can be true – the use of other drugs can lead to nicotine addiction.
So Dr Steven Goldberg, of the National Institute on Drug Abuse, Baltimore, Maryland, and colleagues tested whether exposing rats to THC would make them more likely to self administer nicotine.
For three days, one group was given twice daily injections of the chemical while another received an equivalent dose of an inactive placebo.
Beginning a week after their final jab, the rats were trained to work for intravenous injections of nicotine.
Those previously given THC were far more likely to self-administer nicotine than the others, the researchers found.
In addition, the THC-exposed rats were prepared to work much harder to obtain nicotine than the control group, suggesting the value of nicotine was far greater after THC exposure.
Dr Goldberg said: 'This finding indicates THC-exposed rats placed a higher value on nicotine and devoted more time and energy to acquiring the drug.'
Cigarettes are often considered a 'gateway' to other drugs such as marijuana (pictured), but there is now evidence to show the reverse can be true
Although there are many factors that may contribute to a progression from marijuana use to tobacco dependence, the research suggests lasting effects of THC may make marijuana users more susceptible to the addictive effects of tobacco.
Dr Goldberg said: 'Tobacco is considered a gateway drug because its use tends to precede the use of other drugs.
'However, there is epidemiological evidence that cannabis use develops prior to tobacco use in a substantial number of cases, and cannabis use by teenagers increases the likelihood of developing tobacco dependence when they reach young adulthood.
'While there is also evidence genetic, social and environmental factors encourage the co-use of cannabis and tobacco, findings that cannabis use sometimes precedes regular tobacco use raise the possibility THC exposure might increase susceptibility to nicotine addiction.'
He added: 'It is estimated cigarette smoking will kill half of all lifetime users. In this context, an increased risk of tobacco dependence might be the most important health consequence of cannabis use.'
Previous research involving 2,500 young people in Australia found those who smoked cannabis daily for at least a month were four times more likely to become addicted to nicotine by the time they reached their 20s.