This is what I had in mind:
Addictive Potential
Long-term marijuana abuse can lead to addiction for some people; that is, they abuse the drug compulsively even though it interferes with family, school, work, and recreational activities.
Drug craving and withdrawal symptoms can make it hard for long-term marijuana smokers to stop abusing the drug. People trying to quit report irritability, sleeplessness, and anxiety32. They also display increased aggression on psychological tests, peaking approximately one week after the last use of the drug33.
http://www.nida.nih.gov/Infofacts/marijuana.html