Why teenagers should steer clear of cannabis

Adolescents' use of marijuana may increase the risk of heroin addiction later in life, a new study suggests. Researchers say the work adds to "overwhelming" evidence that people under 21 should not use marijuana because of the risk of damaging the developing brain. The idea that smoking cannabis increases the user's chance of going on to take harder drugs such as heroin is highly contentious.

http://www.newscientist.com/article/
dn9488-why-teenagers-should-steer-clear-of-cannabis.html