ABSTRACT

Information on the adverse effects of cannabis has accrued over the past few decades in a piecemeal fashion. Unfortunately, systematic, well-conducted research on the toxicology of the drug in humans is comparatively rare. In most cases, animal studies are of dubious relevance to human toxicology, and this review concentrates almost exclusively on investigations involving humans. Most information has come from small scale investigations, case reports and anecdotal evidence. Many studies assume that the adverse effects of smoking cannabis and the adverse effects of oral or intravenous delta-9tetrahydrocannabinol or THC (the main psychoactive constituent) are equivalent. This is not necessarily correct since, as discussed in other chapters, there are many other cannabinoids present in the plant. In addition, certain adverse effects of cannabis may depend upon the route of administration. Smoking gives rise to very rapid, and high, plasma and CNS levels of THC. This, for example, produces a different quality of psychoactive effect to that produced by oral administration which has a slow onset, but provides more sustained plasma levels of THC. Smoked cannabis produces adverse effects upon the lungs which do not occur when THC is given orally.