[Flashback following use of cannabis--a review]

The present study tries to find an answer to the question, whether the consumption of cannabis can cause flashbacks, and, if so, under what circumstances they occur. This is of interest for the treatment, prognosis and also from the legal viewpoint. The definition of a flashback is often unclear. Empirical investigations are often not sufficiently comparable, the supplementary data are very often missing, making the evaluation of the results difficult. Self-diagnosis by the consumer is usually unsuitable for estimating the frequency and phenomenology of flashbacks. Cannabis may trigger flashbacks after consuming hallucinogenes; the probability of the occurrence of a flashback seems to increase with the amount of hallucinogenes a person has consumed. A definite correlation between the amount of hashish consumed and the occurrence of flashback does not exist. Flashbacks have also been reported after consuming cannabis alone. However, data vary regarding the frequency of such flashbacks. According to the available data they occur rarely and require a thorough differential diagnostic evaluation in each individual case. As a rule, the occurrence of a flashback may take place in cases where there is an intake of hallucinogenic drugs in the recent case history.