False, it protects and heals the brain.

Marijuana, Memory, and the Hippocampus Memory impairment from marijuana use occurs because THC alters how information is processed in the hippocampus, a brain area responsible for memory formation. This is an image of a rat brain with the different parts of the brain labeled. Distribution of cannabinoid receptors in the rat brain. Brain image reveals high levels (shown in orange and yellow) of cannabinoid receptors in many areas, including the cortex, hippocampus, cerebellum, and nucleus accumbens (ventral striatum). Most of the evidence supporting this assertion comes from animal studies. For example, rats exposed to THC in utero, soon after birth, or during adolescence, show notable problems with specific learning/memory tasks later in life. Moreover, cognitive impairment in adult rats is associated with structural and functional changes in the hippocampus from THC exposure during adolescence. As people age, they lose neurons in the hippocampus, which decreases their ability to learn new information. Chronic THC exposure may hasten age-related loss of hippocampal neurons. In one study, rats exposed to THC every day for 8 months (approximately 30 percent of their life-span) showed a level of nerve cell loss (at 11 to 12 months of age) that equaled that of unexposed animals twice their age.

Short-term memory is impacted TEMPORARILY while high, due to the biology of the brain. It has no negative effects and cannabis actually improves long-term memory.

Wrong, Marijuana "impersonates" natural cabenoids within the brain, clogging receptors and causing overproduction of hormones that cause hunger and other impared mental function, including impared judgement.