Marijuana, which comes from the hemp plant Cannabis sativa, is the most frequently used illegal drug in the U.S. About 4% of American adults smoke pot at least once a year. Roughly 1% of adults abuse pot, and one in 300 have a pot addiction.
Most people smoke the plant's dried leaves, flowers, stems, and seeds. But marijuana also can be mixed into food or brewed as a tea. Marijuana goes by many street names, including pot, weed, and herb. Hash, a concentrated form of the drug, is short for hashish.
The rates of marijuana smoking in adults have remained stable since the 1990s. However, the rates of addiction to pot have risen significantly over that same period. And, according to recent government studies, as many as 30% of today's teenagers are smoking marijuana.
Occasional marijuana use is rarely seriously harmful, but smoking pot has important medical effects.
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Physiological Effects of Marijuana
The active ingredient in marijuana is THC. That's short for delta-9-tetrahydrocannabinol.
THC is rapidly absorbed after smoking pot. Within minutes, THC
and the other substances in marijuana smoke cause short-term medical
effects.
Signs of using marijuana include:
- Rapid heart rate
- Increased blood pressure
- Increased rate of breathing
- Red eyes
- Dry mouth
- Increased appetite, or "the munchies"
- Slowed reaction time
Biochemical mechanisms in the brain
In 1990 the discovery of cannabinoid receptors located throughout the brain and body, along with endogenous cannabinoid neurotransmitters like anandamide (a lipid material derived ligand from arachidonic acid), suggested that the use of cannabis affects the brain in the same manner as a naturally occurring brain chemical.[citation needed] Cannabinoids usually contain a 1,1'-di-methyl-pyrane ring, a variedly derivatized aromatic ring and a variedly unsaturated cyclohexyl ring and their immediate chemical precursors, constituting a family of about 60 bi-cyclic and tri-cyclic compounds. Like most other neurological processes, the effects of cannabis on the brain follow the standard protocol of signal transduction, the electrochemical system of sending signals through neurons for a biological response. It is now understood that cannabinoid receptors appear in similar forms in most vertebrates and invertebrates and have a long evolutionary history of 500 million years. The binding of cannabinoids to cannabinoid receptors decrease adenylyl cyclase activity, inhibit calcium N channels, and disinhibit K+A channels. There are two types of cannabinoid receptors (CB1 and CB2).
The CB1 receptor is found primarily in the brain and mediates the psychological effects of THC. The CB2 receptor is most abundantly found on cells of the immune system. Cannabinoids act as immunomodulators at CB2 receptors, meaning they increase some immune responses and decrease others. For example, nonpsychotropic cannabinoids can be used as a very effective anti-inflammatory. The affinity of cannabinoids to bind to either receptor is about the same, with only a slight increase observed with the plant-derived compound CBD binding to CB2 receptors more frequently. Cannabinoids likely have a role in the brain’s control of movement and memory, as well as natural pain modulation. It is clear that cannabinoids can affect pain transmission and, specifically, that cannabinoids interact with the brain's endogenous opioid system and may affect dopamine transmission. This is an important physiological pathway for the medical treatment of pain.
Sustainability in the body
Most cannabinoids are lipophilic (fat soluble) compounds that are easily stored in fat, thus yielding a long elimination half-life relative to other recreational drugs. The THC molecule, and related compounds, are usually detectable in drug tests from 3 days up to 10 days according to Redwood Laboratories; heavy users can produce positive tests for up to 3 months after ceasing cannabis use (see drug test).
Short-term effects
When smoked, the short-term effects of cannabis manifest within seconds and are fully apparent within a few minutes, typically lasting for 1-3 hours, varying by the person and the strain of marijuana. The duration of noticeable effects has been observed to diminish due to prolonged, repeated use and the development of a tolerance to cannabinoids.
Smoked
A study of ten healthy, robust, male volunteers who resided in a residential research facility sought to examine both acute and residual subjective, physiologic, and performance effects of smoking marijuana cigarettes. On three separate days, subjects smoked one NIDA marijuana cigarette containing either 0%, 1.8%, or 3.6% THC, documenting subjective, physiologic, and performance measures prior to smoking, five times following smoking on that day, and three times on the following morning. Subjects reported robust subjective effects following both active doses of marijuana, which returned to baseline levels within 3.5 hours. Heart rate increased and the pupillary light reflex decreased following active dose administration with return to baseline on that day. Additionally, marijuana smoking acutely produced decrements in smooth pursuit eye tracking. Although robust acute effects of marijuana were found on subjective and physiological measures, no effects were evident the day following administration, indicating that the residual effects of smoking a single marijuana cigarette are minimal.
Oral
When taken orally, the psychoactive effects take longer to manifest and generally last longer, typically lasting for 4–10 hours after consumption. Very high doses may last even longer. Also, oral ingestion use eliminates the need to inhale toxic combustion products created by smoking and therefore reduces the risk of respiratory harm associated with cannabis smoking.
Neurological effects
The areas of the brain where cannabinoid receptors are most prevalently located are consistent with the behavioral effects produced by cannabinoids. Brain regions in which cannabinoid receptors are very abundant are the basal ganglia, associated with movement control; the cerebellum, associated with body movement coordination; the hippocampus, associated with learning, memory, and stress control; the cerebral cortex, associated with higher cognitive functions; and the nucleus accumbens, regarded as the reward center of the brain. Other regions where cannabinoid receptors are moderately concentrated are the hypothalamus, which regulates homeostatic functions; the amygdala, associated with emotional responses and fears; the spinal cord, associated with peripheral sensations like pain; the brain stem, associated with sleep, arousal, and motor control; and the nucleus of the solitary tract, associated with visceral sensations like nausea and vomiting.
Most notably, the two areas of motor control and memory are where the effects of cannabis are directly and irrefutably evident. Cannabinoids, depending on the dose, inhibit the transmission of neural signals through the basal ganglia and cerebellum. At lower doses, cannabinoids seem to stimulate locomotion while greater doses inhibit it, most commonly manifested by lack of steadiness (body sway and hand steadiness) in motor tasks that require a lot of attention. Other brain regions, like the cortex, the cerebellum, and the neural pathway from cortex to striatum, are also involved in the control of movement and contain abundant cannabinoid receptors, indicating their possible involvement as well.
Experiments on animal and human tissue have demonstrated a disruption of short-term memory formation, which is consistent with the abundance of CB1 receptors on the hippocampus, the region of the brain most closely associated with memory. Cannabinoids inhibit the release of several neurotransmitters in the hippocampus such as acetylcholine, norepinephrine, and glutamate, resulting in a major decrease in neuronal activity in that region. This decrease in activity resembles a "temporary hippocampal lesion.
Effects on driving
Cannabis usage has been shown to negatively affect the ability to drive. The British Medical Journal recently indicated that "Drivers who consume cannabis within three hours of driving are nearly twice as likely to cause a vehicle collision as those who are not under the influence of drugs or alcohol"
An older 2001 study by the United Kingdom Transit Research Laboratory (TRL) also focused on the effects of cannabis use on driving. The report summarizes current knowledge about the effects of cannabis on driving and accident risk based on a review of available literature published since 1994 and the effects of cannabis on laboratory based tasks. The study identified young males, amongst whom cannabis consumption is frequent and increasing, and in whom alcohol consumption is also common, as a risk group for traffic accidents. This is due to driving inexperience and factors associated with youth relating to risk taking, delinquency and motivation. These demographic and psychosocial variables may relate to both drug use and accident risk, thereby presenting an artificial relationship between use of drugs and accident involvement.
The effects of cannabis on laboratory-based tasks show clear impairment with respect to tracking ability, attention, and other tasks depending on the dose administered. Both simulation and road trials generally find that driving behavior shortly after consumption of larger doses of cannabis results in:
increased variability in lane position (such as taking a curve too tightly or too loosely).
longer decision times, leading to slower responses to driving situation.
Vascular effectsCannabis arteritis is a very rare peripheral vascular disease similar to Buerger's disease. There were about 50 confirmed cases from 1960 to 2008, all of which occurred in Europe. However, all of the cases also involved tobacco[citation needed] (a known cause of Buerger's disease) in one way or another, and nearly all of the cannabis use was quite heavy,A 2008 study by the National Institutes of Health Biomedical Research Centre in Baltimore found that heavy, chronic smoking of marijuana (138 joints per week) changed blood proteins associated with heart disease and stroke.[52] This may be a result of raised carboxyhemoglobin levels from carbon monoxide. A similar increase in heart disease and ischemic strokes is observed in tobacco smokers, which suggests that the harmful effects come from combustion products, not marijuana.
Memory and learning
Studies on cannabis and memory are hindered by small sample sizes, confounding drug use, and other factors. The strongest evidence regarding cannabis and memory focuses on its short-term negative effects on short-term and working memory.
A 2008 review of the evidence surrounding the acute impact on memory concluded that cannabinoids impair all aspects of short-term memory, especially short-term episodic and working memory. One small study found that no learning occurred during the 2 hour period in which the subjects (infrequent users) were "stoned"
Appetite
The feeling of increased appetite following the use of cannabis has been documented for hundreds of years, and is known as "the munchies" in popular culture. Clinical studies and survey data have found that cannabis increases food enjoyment and interest in food. Scientists have claimed to be able to explain what causes the increase in appetite, concluding that "endocannabinoids in the hypothalamus activate cannabinoid receptors that are responsible for maintaining food intake". Rarely, chronic users experience a severe vomiting disorder, cannabinoid hyperemesis syndrome, after smoking and find relief by taking hot baths.
Effects in pregnancy
A study of 600 mothers that reported smoking cannabis during pregnancy suggested that it was not associated with increased risk of perinatal mortality. However, frequent and regular use of cannabis throughout pregnancy may be associated with a small but statistically detectable decrease in birth weight .
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