"171 How Does Marijuana Affect the Brain? Scientists have learned a great deal about how THC acts in the brain to produce its many effects. When someone smokes marijuana, THC rapidly passes from the lungs into the b loodstream, which carries the chemical to the brain and other organs throughout the body. THC acts upon specific sites in the brain, called cannabinoid receptors, kicking off a series of cellular reactions that ultimately lead to the \"high\" that users expe rience when they smoke marijuana. Some brain areas have many cannabinoid receptors; others have few or none. The highest density of cannabinoid receptors are found in parts of the brain that influence pleasure, memory, thinking, concentrating, sensory and time perception, and coordinated movement. Not surprisingly, marijuana intoxication can cause distorted perceptions, impaired coordination, difficulty with thinking and problem solving, and problems with learning and memory. Research has shown that, in chr onic users, marijuana's adverse impact on learning and memory can last for days or weeks after the acute effects of the drug wear off. As a result, someone who smokes marijuana every day may be functioning at a suboptimal intellectual level all of the time . Research into the effects of long - term cannabis use on the structure of the brain has yielded inconsistent results. It may be that the effects are too subtle for reliable detection by current techniques. A similar challenge arises in studies of the effec ts of chronic marijuana use on brain function. Brain imaging studies in chronic users tend to show some consistent alterations, but their connection to impaired cognitive functioning is far from clear. This uncertainty may stem from confounding factors suc h as other drug use, residual drug effects, or withdrawal symptoms in long - term chronic users. What Other Adverse Effect Does Marijuana Have on Health? 1. Effects on the Heart : Marijuana increases heart rate by 20 - 100 percent shortly after smoking; this effe ct can last up to 3 hours. In one study, it was estimated that marijuana users have a 4.8 - fold increase in the risk of heart attack in the first hour after smoking the drug. This may be due to increased heart rate as well as the effects of marijuana on hea rt rhythms, causing palpitations and arrhythmias. This risk may be greater in aging populations or in those with cardiac vulnerabilities. 2. Effects on the Lungs : Numerous studies have shown marijuana smoke to contain carcinogens and to be an irritant to the lungs. In fact, marijuana smoke contains 50 - 70 percent more carcinogenic hydrocarbons than tobacco smoke. Marijuana users usually inhale more deeply and hold their breath longer than tobacco smokers do, which further increase the lungs' exposure to carcin ogenic smoke. Marijuana smokers show dysregulated growth of epithelial cells in their lung tissue, which could lead to cancer; however, a recent case - controlled study found no positive associations between marijuana use and lung, upper respiratory, or uppe r digestive tract cancers. Thus, the link between marijuana smoking and these cancers remains unsubstantiated at this time. Nonetheless, marijuana smokers can have many of the same respiratory problems"