Elevated Plasma Dopamine Metabolites in Cannabis Psychosis

To The Editor: Cannabis has received increasing attention as a risk factor for the development of psychotic states (1) . There are relatively little data related to the biochemical profile in cannabis psychosis (2, 3) . We report on five consecutive cases of first-admission psychosis associated with documented cannabis use. For comparison, we used a consecutive series of first-admission psychosis and a group of nonpsychotic inpatients treated during the same period. We collected plasma for homovanillic acid on the first morning after admission following an overnight fast.

To our knowledge, this is the first report of elevated plasma homovanillic acid in cannabis-related psychosis, although we are aware of a report of elevated urinary homovanillic acid following cannabis administration to a volunteer population (2) .

In this small case series of patients with first-episode psychosis associated with cannabis use, plasma homovanillic acid was significantly higher than values for each of the comparison groups. There are several possibilities for this result. First, plasma homovanillic acid is elevated in a number of newly admitted psychosis patients (4), which was the case in our first-episode psychosis group. However, plasma homovanillic acid was even higher in the cannabis group. Second, acute cannabis administration can produce increased dopamine activity in animals and humans (2, 3) . Third, individuals with cannabis psychosis may also have a genetic vulnerability that can lead to increased dopaminergic activity (1) .