Neurological effects of cannabis.The areas of the brain where cannabis 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, like acetylcholine, norepinephrine, and glutamate, resulting in a major decrease in neuronal activity in that region. This decrease in activity resembles a “temporary hippocampal lesion.” In the end, this procedure could lead to the blocking of cellular processes that are associated with memory formation.
In in-vitro experiments THC at extremely high concentrations, which could not be reached with commonly consumed doses, caused competitive inhibition of the AChE enzyme and inhibition of β-amyloid peptide aggregation, Implicated in the development of Alzheimer’s disease. Compared to currently approved drugs prescribed for the treatment of Alzheimer’s disease, THC is a considerably superior inhibitor of A aggregation, and this study provides a previously unrecognized molecular mechanism through which cannabinoid molecules may impact the progression of this debilitating disease.
 Effects on driving
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A 2001 study by the United Kingdom Transit Research Laboratory (TRL) specifically focuses on the effects of cannabis use on driving, and is one of the most recent and commonly quoted studies on the subject. 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 situations
Kelly, Darke and Ross show similar results, with laboratory studies examining the effects of cannabis on skills utilised while driving showing impairments in tracking, attention, reaction time, short-term memory, hand-eye coordination, vigilance, time and distance perception, and decision making and concentration. An EMCDDA review concluded that “the acute effect of moderate or higher doses of cannabis impairs the skills related to safe driving and injury risk”, specifically “attention, tracking and psychomotor skills”. In their review of driving simulator studies, Kelly et al. conclude that there is evidence of dose-dependent impairments in cannabis-affected drivers’ ability to control a vehicle in the areas of steering, headway control, speed variability, car following, reaction time and lane positioning. The researchers note that “even in those who learn to compensate for a drug’s impairing effects, substantial impairment in performance can still be observed under conditions of general task performance (i.e. when no contingencies are present to maintain compensated performance).”
 Vascular effects of cannabis
Cannabis 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 (a known cause of Buerger’s disease) in one way or another, and nearly all of the cannabis use was quite heavy. In Europe, cannabis is typically mixed with tobacco, in contrast to North America.
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. This is 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.
A 2005 article in the Journal of Neurology, Neurosurgery and Psychiatry reported on a 36-year-old man who suffered a stroke on three separate occasions after smoking a large amount of marijuana, despite having no known risk factors for the disorder, suggesting that a rare side effect of marijuana use may be an increase in the incidence of strokes among young smokers. A 2000 study by researchers at Boston’s Beth Israel Deaconess Medical Center, Massachusetts General Hospital and Harvard School of Public Health also found that a middle-age person’s risk of heart attack rises nearly fivefold in the first hour after smoking marijuana, about the same elevated risk as vigorous exercise or sexual intercourse.
 Adulterated cannabis
Contaminants may be found in hashish obtained from “soap bar”-type sources. The dried flowers of the plant may be contaminated by the plant taking up heavy metals and other toxins from its growing environment, or by the addition of lead or glass beads, used to increase the weight or to make the cannabis appear as if it has more crystal-looking trichomes indicating a higher THC content. Users who burn hot or mix cannabis with tobacco are at risk of failing to detect deviations from appropriate cannabis taste.
Despite cannabis being generally perceived as a natural or “chemical-free” product, in a recent Australian survey one in four Australians consider cannabis grown indoors under hydroponic conditions to be a greater health risk due to increased contamination, added to the plant during cultivation to enhance the plant growth and quality.
 Combination with other drugs
The most obvious confounding factor in cannabis research is the prevalent usage of other recreational drugs, especially alcohol and nicotine. Such complications demonstrate the need for studies on cannabis that have stronger controls, and investigations into alleged symptoms of cannabis use that may also be caused by tobacco. Some critics question whether agencies doing the research make an honest effort to present an accurate, unbiased summary of the evidence, or whether they “cherry-pick” their data to please funding sources which may include the tobacco industry or governments dependent on cigarette tax revenue; others caution that the raw data, and not the final conclusions, are what should be examined.
Cannabis also has been shown to have a synergistic cytotoxic effect on lung cancer cell cultures in vitro with the food additive butylated hydroxyanisole (BHA) and possibly the related compound butylated hydroxytoluene (BHT). The study concluded, “Exposure to marijuana smoke in conjunction with BHA, a common food additive, may promote deleterious health effects in the lung.” BHA & BHT are human-made fat preservatives, and are found in many packaged foods including: plastics in boxed cereal, Jello, Slim Jims, and more.[further explanation needed]
The Australian National Household Survey of 2001 showed that cannabis use in Australia is rarely used without other drugs. 95% of cannabis users also drank alcohol; 26% took amphetamines; 19% took ecstasy and only 2.7% reported not having used any other drug with cannabis. While research has been undertaken on the combined effects of alcohol and cannabis on performing certain tasks, little research has been conducted on the reasons why this combination is so popular. Evidence from a controlled experimental study undertaken by Lukas and Orozco suggests that alcohol causes THC to be absorbed more rapidly into the blood plasma of the user. Data from the Australian National Survey of Mental Health and Wellbeing found that three-quarters of recent cannabis users reported using alcohol when cannabis was not available.
 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”.
Researchers find many harmful effects of cannibis