Marijuana, derived from the hemp, Cannabis sativa, is the most frequently used illegal substance in the United States, where it continues to be a controversial topic of legal debate. Marijuana has many slang names, such as pot, weed and grass. According to the National Institute on Drug Abuse (NIDA), in 2007 nearly 6,000 people per day tried marijuana; and, of special concern, more than 62 percent were under 18 years, which indicates marijuana's continued experimentation among youth. Of 400 chemicals in this substance, delta-9-tetrahydrocannabinol (THC) is responsible for marijuana's effects on the brain.
Upon inhaling marijuana, THC quickly gets transported from the respiratory system to the circulatory system and enters the blood. Consequently, the blood transports THC to the brain and elsewhere throughout the entire body. Different areas of the brain have varying quantities of receptors (for cannabinoid) on neurons (brain nerve cells) which are affected by THC as they bind with the THC chemical; for example, areas with multiple such receptors include thinking ability and concentration, sensory perception as well as perception of time, areas of memory, pleasure and coordination.
Almost immediately after first smoking marijuana the effects begin and may continue as long as two or three hours. A burning sensation in the mouth, a dry throat, bloodshot eyes and increased appetite are common. Also, consistent with brain areas most affected, short-term effects may include impairments in thinking, problem-solving, judgment and comprehension, as well as impaired short-term memory. Time perception is altered and behaviors become limited due to impaired speech, concentration and coordination abilities. Sensory perception becomes distorted in terms of vision, hearing and touch. Physiologically, marijuana lowers blood pressure while increasing heart rate by 20 to 100 percent, which can last up to three hours. This drop in blood pressure, combined with an increased heart rate, is serious because, as the NIDA reports, a person smoking marijuana has four times the risk of experiencing a myocardial infarction (heart attack) within the first hour after inhalation. Moreover, while this substance is known for its euphoric state or sleepiness, it also can produce anxiety, paranoia with hallucinations or panic attacks.
Chronic use of marijuana may produce multiple health problems later on in life beyond addiction to the substance itself. For example, chronic use is associated with high scores for anxiety and depression, with increased suicidal thinking patterns as well as the diagnosis of schizophrenia. Another important long-term effect is how THC acts on the immune system, that is, it decreases the function of the immune system, which may leave you more susceptible to frequent illnesses and infections. In terms of respiratory effects, marijuana is more potent than tobacco because, as the NIDA states, it has 50 to 70 percent more carcinogenic properties than tobacco; thus, it may increase the likelihood of developing lung cancer or at least increased susceptibility to frequent lung infections or obstructed airway conditions. Sexual dysfunction also may be a long-term effect.