A review of the published literature into cannabis withdrawal symptoms in human users.

Recent experimental papers have been published suggesting the appearance of withdrawal symptoms upon the cessation of cannabis use in human users and proposing the introduction of a diagnostic category for such symptoms. Research also continues to be published into the physiological effects of cannabis on animals via self-administration paradigms and the use of cannabinoid antagonists. Animal research does not provide a clear picture of a consistent withdrawal effect. The literature on withdrawal symptoms appearing in human users following the cessation of cannabis is investigated in this paper to clarify this issue further and enhance the scientific and lay debate on the status of the drug. Methodological weaknesses in the literature are highlighted. These include variable levels of drug-dose administered in laboratory conditions, lack of controlled studies and the absence of definitions of the withdrawal syndrome sought. It is suggested that the studies conducted to date do not provide a strong evidence base for the drawing of any conclusions as to the existence of a cannabis withdrawal syndrome in human users, or as to the cause of symptoms reported by those abstaining from the drug. On the basis of current research cannabis cannot be said to provide as clear a withdrawal pattern as other drugs of abuse, such as opiates. However, cannabis also highlights the need for a further defining of withdrawal, in particular the position that rebound effects occupy in this phenomenon. It is concluded that more controlled research might uncover a diagnosable withdrawal syndrome in human users and that there may be a precedent for the introduction of a cannabis withdrawal syndrome before the exact root of it is known.