Background: Cannabis (Marijuana) is one of the most widely used illicit drugs around the world. In the United States, it is the most commonly-used illicit drug. While there have been increasing numbers of arguments about legalizing marijuana primarily for its medicinal and recreational use, there remain concerns about its impact on the brain: neuropsychiatric problems, in particular, from its chronic use. Purpose & Method:To highlight recent knowledge, understanding and research of marijuana, its potency, mechanism of action, effects on psychomotor and cognitive performance and other neuropsychiatric function are explored; paying particular attention to the long term effects of Marijuana usage. Marijuana interacts with endogenous cannabinoid (CB) systems in the body. Actions on specific brain receptors are reflected in CB dose-related impairments of psychomotor performance. Further effects relating to psychosis, memory problems, and depression, are also experienced; primarily as a result of cortex degeneration. Conclusion:Marijuana significantly impacts the brain, specifically, the brain's structure, function and connectivity. Although marijuana use is linked to many neurological and psychiatric effects from long term use, it is often perceived in society as harmless