Here's Why Marijuana Impairs Memory Formation

Scientists have known for some time that marijuana impairs the ability to convert short-term or working memories into lasting form. Now they know why. The protein synthesis machinery in the hippocampus is necessary to accomplish lasting memory formation, and a study of mouse hippocampus revealed that marijuana impairs the protein synthesis pathway responsible for memory consolidation.

Source:
Puighermannal, E. et al. 2009. Cannabinoid modulation of hippocampal long-term memory is mediated by mTOR signaling. Nature Neuroscience. On-line edition, Aug. 2; doi:10.1038/nn.2369