Cannabis is widely used recreationally and for symptomatic relief in a number of ailments. However, cannabis has been implicated as a risk factor for the development of psychotic illness. For forty years researchers have utilised intravenous preparations of Δ(9)-THC, as well as several other phytocannabinoids, in a laboratory setting. The intravenous route has the most reliable pharmacokinetics, reducing inter-individual variation in bioavailability and is well suited for the delivery of synthetic compounds containing a sole pharmacological moiety. Given the association between cannabinoids and psychotic illness, there has been a resurgence of interest in experimental studies of cannabinoids in humans, and the intravenous route has been employed. Here in a critical review, we appraise the major findings from recent intravenous cannabinoid studies in humans and trace the historical roots of this work back to the 1970's.