Chronic cannabis use produces effects within the central nervous system (CNS) which include deficits in learning and attention tasks and decreased brain volume. Neurotrophins, in particular nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF), are proteins that serve as survival factors for CNS neurons. Deficits in the production and utilization of these proteins can lead to CNS dysfunctions including those associated with cannabis abuse. In this study we measured by enzyme-linked immunosorbent assay (ELISA) the NGF and BDNF serum levels in two groups of subjects: cannabis-dependent patients and healthy subjects. We found that NGF serum levels were significantly reduced in cannabis abusers as compared to healthy subjects. These findings indicate that NGF may have a role in the central action of cannabis and potentially in the neurotoxicity induced by this drug. These data also suggest that chronic cannabis consumption may be a risk factor for developing psychosis among drug users.