The bulk of marijuana users does not progress to using other "harder" narcotics such as heroin or cocaine. Nevertheless, according to other studies, people are more likely to use marijuana before attempting other narcotics.  Animal studies have also shown that when rodents are administered multiple doses of THC, they have heightened behavioral responses and changed neural activity not only when given more THC, but when given other medications like morphine. Researchers are currently investigating if a teen's exposure to marijuana causes brain alterations that make them more prone to get addicted to weed or other drugs like alcohol, opiates, or cocaine.