For many years it was assumed that cannabis was not an addictive substance. This view was based on the apparent lack of a cannabis withdrawal syndrome. The absence of a withdrawal syndrome was said to distinguish cannabis from ‘hard drugs’, such as opiates and cocaine, and even from the two most widely used ‘soft drugs’, nicotine and alcohol.

Recently a number of studies have established that a cannabis withdrawal syndrome does indeed exist. In the latest of these, 49 users agreed to try a 2-week cannabis free period.

http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0044864

As in previous work, participants reported a number of symptoms during abstinence. Symptoms included difficulty sleeping, anxiety, mood swings, physical tension, stomach pain and craving. Symptoms peaked at around 4 days and then gradually decreased over the next 10 days. 

Notably, those who experienced the most severe withdrawal symptoms were more likely to relapse and begin taking cannabis again. They also experienced more functional impairment during abstinence. 

This study highlights the difficulties people can experience when they attempt to give up cannabis. It also demonstrates that the withdrawal reaction is an important factor in determining whether an attempt at abstinence is likely to be successful.