Marijuana Causes Long-Term Changes
Source: "Dr. Kabran Chapek ... says, 'I'm not surprised when someone with anxiety tells me that they use marijuana or alcohol to help them sleep, or calm their nerves. It's predictably people with over activity in their brains and problems like anxiety or PTSD who use sedating substancesówe can see it on their SPECT scans. The problem with marijuana is that it's not selective.† Not only does it calm the parts of the brain that are overactive, it calms the entire brainólong-termóthrough a slow and insidious process.'" ["Marijuana Causes Long-term Brain Changes", Amen Clinics, 2015 February 06].
Source: "When someone stops using marijuana, significant irritability is common as the temporal lobes regain full functioning.† According to Dr. Chapek, one can expect to see improvements in motivation, concentration, and focus after abstaining for just 2-3 months." ["Marijuana Causes Long-term Brain Changes", Amen Clinics, 2015 February 06].
Source: [FM Fibley, "Marijuana Craving in the Brain", PNAS].
Source: Good summary of the above study. [Aalok Mehta, "Marijuana Craving Affects Brain like Alcohol, Addictive Behaviors", 2009 September 18].