Cannabis

Cannabis (Cán-na-bis) is a genus of flowering plants that includes three putative varieties, Cannabis sativa, Cannabis indica, and Cannabis ruderalis. These three taxa are indigenous to Central Asia, and South Asia. Cannabis has long been used for fibre (hemp), for seed and seed oils, for medicinal purposes, and as a recreational drug. Industrial hemp products are made from Cannabis plants selected to produce an abundance of fiber. To satisfy the UN Narcotics Convention, some hemp varieties have been developed which contain minimal levels of THC (Δ9- tetrahydrocannabinol), one of the psychoactive molecules that produces the "high" associated with marijuana. The psychoactive product consists of dried flowers of plants selectively bred to produce high levels of THC and other psychoactive chemicals. Various extracts including hashish and hash oil are also produced from the plant.

Etymology
The word cannabis is from Greek κάνναβις (kánnabis) (see Latin cannabis), which was originally Scythian or Thracian. It is related to the Persian kanab, the English canvas and possibly even to the English hemp (Old English hænep). In modern Hebrew, qannabōs modern pronunciation:  is used but  maʿăleh ʿāšān modern pronunciation:  (smoke bringer) is the ancient term. Old Akkadian qunnabtu, Neo-Assyrian and Neo-Babylonian qunnabu were used to refer to the plant meaning "a way to produce smoke."

Description
Cannabis is an annual, dioecious, flowering herb. The leaves are palmately compound or digitate, with serrate leaflets. The first pair of leaves usually have a single leaflet, the number gradually increasing up to a maximum of about thirteen leaflets per leaf (usually seven or nine), depending on variety and growing conditions. At the top of a flowering plant, this number again diminishes to a single leaflet per leaf. The lower leaf pairs usually occur in an opposite leaf arrangement and the upper leaf pairs in an alternate arrangement on the main stem of a mature plant.

The leaves have a peculiar and diagnostic venation pattern that enables persons poorly familiar with the plant to distinguish a Cannabis leaf from unrelated species that have confusingly similar leaves (see illustration). As is common in serrated leaves, each serration has a central vein extending to its tip. However,the serration vein originates from lower down the central vein of the leaflet, typically opposite to the position of, not the first notch down, but the next notch. This means that on its way from the midrib of the leaflet to the point of the serration, the vein serving the tip of the serration passes close by the intervening notch. Sometimes the vein will actually pass tangent to the notch, but often it will pass by at a small distance, and when that happens a spur vein (occasionally a pair of such spur veins) branches off and joins the leaf margin at the deepest point of the notch. This venation pattern varies slightly among varieties, but in general it enables one to tell Cannabis leaves from superficially similar leaves without difficulty and without special equipment. Tiny samples of Cannabis plants also can be identified with precision by microscopic examination of leaf cells and similar features, but that requires special expertise and equipment.

Cannabis normally has imperfect flowers, with staminate "male" and pistillate "female" flowers occurring on separate plants. It is not unusual, however, for individual plants to bear both male and female flowers. Although monoecious plants are often referred to as "hermaphrodites," true hermaphrodites (which are less common) bear staminate and pistillate structures on individual flowers, whereas monoecious plants bear male and female flowers at different locations on the same plant. Male flowers are normally borne on loose panicles, and female flowers are borne on racemes. "At a very early period the Chinese recognized the Cannabis plant as dioecious," and the (ca. 3rd century BCE) Erya dictionary defined xi 枲 "male Cannabis" and fu 莩 (or ju 苴) "female Cannabis".

All known strains of Cannabis are wind-pollinated and produce "seeds" that are technically achenes. Most strains of Cannabis are short day plants, with the possible exception of C. sativa subsp. sativa var. spontanea (= C. ruderalis), which is commonly described as "auto-flowering" and may be day-neutral.

Cannabis, like many organisms, is diploid, having a chromosome complement of 2n=20, although polyploid individuals have been artificially produced. The first genome sequence of Cannabis, which is estimated to be 820 Mb in size, was published in 2011 by a team of Canadian scientists. The plant is believed to have originated in the mountainous regions northwest of the Himalayas. It is also known as hemp, although this term is often used to refer only to varieties of Cannabis cultivated for non-drug use. Cannabis plants produce a group of chemicals called cannabinoids, which produce mental and physical effects when consumed.

Cannabinoids, terpenoids, and other compounds are secreted by glandular trichomes that occur most abundantly on the floral calyxes and bracts of female plants. As a drug it usually comes in the form of dried flower buds (marijuana), resin (hashish), or various extracts collectively known as hashish oil. In the early 20th century, it became illegal in most of the world to cultivate or possess Cannabis for sale or personal use.

Taxonomy
The genus Cannabis was formerly placed in the Nettle (Urticaceae) or Mulberry (Moraceae) family, and later, along with the Humulus genus (hops), in a separate family, the Hemp family (Cannabaceae sensu stricto). Recent phylogenetic studies based on cpDNA restriction site analysis and gene sequencing strongly suggest that the Cannabaceae sensu stricto arose from within the former Celtidaceae family, and that the two families should be merged to form a single monophyletic family, the Cannabaceae sensu lato.

Various types of Cannabis have been described, and variously classified as species, subspecies, or varieties:
 * plants cultivated for fiber and seed production, described as low-intoxicant, non-drug, or fiber types.
 * plants cultivated for drug production, described as high-intoxicant or drug types.
 * escaped, hybridised, or wild forms of either of the above types.

Cannabis plants produce a unique family of terpeno-phenolic compounds called cannabinoids, which produce the "high" one experiences from consuming marijuana. The two cannabinoids usually produced in greatest abundance are cannabidiol (CBD) and/or Δ9-tetrahydrocannabinol (THC), but only THC is psychoactive. Since the early 1970s, Cannabis plants have been categorized by their chemical phenotype or "chemotype," based on the overall amount of THC produced, and on the ratio of THC to CBD. Although overall cannabinoid production is influenced by environmental factors, the THC/CBD ratio is genetically determined and remains fixed throughout the life of a plant. Non-drug plants produce relatively low levels of THC and high levels of CBD, while drug plants produce high levels of THC and low levels of CBD. When plants of these two chemotypes cross-pollinate, the plants in the first filial (F1) generation have an intermediate chemotype and produce similar amounts of CBD and THC. Female plants of this chemotype may produce enough THC to be utilized for drug production.

Whether the drug and non-drug, cultivated and wild types of Cannabis constitute a single, highly variable species, or the genus is polytypic with more than one species, has been a subject of debate for well over two centuries. This is a contentious issue because there is no universally accepted definition of a species. One widely applied criterion for species recognition is that species are "groups of actually or potentially interbreeding natural populations which are reproductively isolated from other such groups." Populations that are physiologically capable of interbreeding, but morphologically or genetically divergent and isolated by geography or ecology, are sometimes considered to be separate species. Physiological barriers to reproduction are not known to occur within Cannabis, and plants from widely divergent sources are interfertile. However, physical barriers to gene exchange (such as the Himalayan mountain range) might have enabled Cannabis gene pools to diverge before the onset of human intervention, resulting in speciation. It remains controversial whether sufficient morphological and genetic divergence occurs within the genus as a result of geographical or ecological isolation to justify recognition of more than one species.

Difference between Cannabis indica and sativa
A Cannabis sativa plant may have a CBD/THC ratio 4:-5 times that of Cannabis Indica. Marijuana with relatively high ratios of CBD:THC is less likely to induce anxiety than vice versa. This might partially be due to CBD's antagonist effects at the cannabinoid receptor, compared to THC's partial agonist effect. The relatively large amount of CBD contained in Cannabis Sativa, means, compared to an Indica, the effects are modulated significantly. The effects of Sativa are well known for its cerebral high, hence used daytime as medical cannabis, while Indica are well known for its sedative effects and preferred night time as medical cannabis.

Early classifications


The Cannabis genus was first classified using the "modern" system of taxonomic nomenclature by Carolus Linnaeus in 1753, who devised the system still in use for the naming of species. He considered the genus to be monotypic, having just a single species that he named Cannabis sativa L. (L. stands for Linnaeus, and indicates the authority who first named the species). Linnaeus was familiar with European hemp, which was widely cultivated at the time. In 1785, noted evolutionary biologist Jean-Baptiste de Lamarck published a description of a second species of Cannabis, which he named Cannabis indica Lam. Lamarck based his description of the newly named species on plant specimens collected in India. He described C. indica as having poorer fiber quality than C. sativa, but greater utility as an inebriant. Additional Cannabis species were proposed in the 19th century, including strains from China and Vietnam (Indo-China) assigned the names Cannabis chinensis Delile, and Cannabis gigantea Delile ex Vilmorin. However, many taxonomists found these putative species difficult to distinguish. In the early 20th century, the single-species concept was still widely accepted, except in the Soviet Union where Cannabis continued to be the subject of active taxonomic study. The name Cannabis indica was listed in various Pharmacopoeias, and was widely used to designate Cannabis suitable for the manufacture of medicinal preparations.

20th century
In 1924, Russian botanist D.E. Janichevsky concluded that ruderal Cannabis in central Russia is either a variety of C. sativa or a separate species, and proposed C. sativa L. var. ruderalis Janisch. and Cannabis ruderalis Janisch. as alternative names. In 1929, renowned plant explorer Nikolai Vavilov assigned wild or feral populations of Cannabis in Afghanistan to C. indica Lam. var. kafiristanica Vav., and ruderal populations in Europe to C. sativa L. var. spontanea Vav. In 1940, Russian botanists Serebriakova and Sizov proposed a complex classification in which they also recognized C. sativa and C. indica as separate species. Within C. sativa they recognized two subspecies: C. sativa L. subsp. culta Serebr. (consisting of cultivated plants), and C. sativa L. subsp. spontanea (Vav.) Serebr. (consisting of wild or feral plants). Serebriakova and Sizov split the two C. sativa subspecies into 13 varieties, including four distinct groups within subspecies culta. However, they did not divide C. indica into subspecies or varieties. This excessive splitting of C. sativa proved too unwieldy, and never gained many adherents.

In the 1970s, the taxonomic classification of Cannabis took on added significance in North America. Laws prohibiting Cannabis in the United States and Canada specifically named products of C. sativa as prohibited materials. Enterprising attorneys for the defense in a few drug busts argued that the seized Cannabis material may not have been C. sativa, and was therefore not prohibited by law. Attorneys on both sides recruited botanists to provide expert testimony. Among those testifying for the prosecution was Dr. Ernest Small, while Dr. Richard E. Schultes and others testified for the defense. The botanists engaged in heated debate (outside of court), and both camps impugned the other's integrity. The defense attorneys were not often successful in winning their case, because the intent of the law was clear.

In 1976, Canadian botanist Ernest Small and American taxonomist Arthur Cronquist published a taxonomic revision that recognizes a single species of Cannabis with two subspecies: C. sativa L. subsp. sativa, and C. sativa L. subsp. indica (Lam.) Small & Cronq. The authors hypothesized that the two subspecies diverged primarily as a result of human selection; C. sativa subsp. sativa was presumably selected for traits that enhance fiber or seed production, whereas C. sativa subsp. indica was primarily selected for drug production. Within these two subspecies, Small and Cronquist described C. sativa L. subsp. sativa var. spontanea Vav. as a wild or escaped variety of low-intoxicant Cannabis, and C. sativa subsp. indica var. kafiristanica (Vav.) Small & Cronq. as a wild or escaped variety of the high-intoxicant type. This classification was based on several factors including interfertility, chromosome uniformity, chemotype, and numerical analysis of phenotypic characters.

Professors William Emboden, Loran Anderson, and Harvard botanist Richard E. Schultes and coworkers also conducted taxonomic studies of Cannabis in the 1970s, and concluded that stable morphological differences exist that support recognition of at least three species, C. sativa, C. indica, and C. ruderalis.   For Schultes, this was a reversal of his previous interpretation that Cannabis is monotypic, with only a single species. According to Schultes' and Anderson's descriptions, C. sativa is tall and laxly branched with relatively narrow leaflets, C. indica is shorter, conical in shape, and has relatively wide leaflets, and C. ruderalis is short, branchless, and grows wild in central Asia. This taxonomic interpretation was embraced by Cannabis aficionados who commonly distinguish narrow-leafed "sativa" drug strains from wide-leafed "indica" drug strains.

Continuing research
Molecular analytical techniques developed in the late 20th century are being applied to questions of taxonomic classification. This has resulted in many reclassifications based on evolutionary systematics. Several studies of Random Amplified Polymorphic DNA (RAPD) and other types of genetic markers have been conducted on drug and fiber strains of Cannabis, primarily for plant breeding and forensic purposes. Dutch Cannabis researcher E.P.M. de Meijer and coworkers described some of their RAPD studies as showing an "extremely high" degree of genetic polymorphism between and within populations, suggesting a high degree of potential variation for selection, even in heavily selected hemp cultivars. They also commented that these analyses confirm the continuity of the Cannabis gene pool throughout the studied accessions, and provide further confirmation that the genus comprises a single species, although theirs was not a systematic study per se.

Karl W. Hillig, a graduate student in the laboratory of long-time Cannabis researcher Paul G. Mahlberg at Indiana University, conducted a systematic investigation of genetic, morphological, and chemotaxonomic variation among 157 Cannabis accessions of known geographic origin, including fiber, drug, and feral populations. In 2004, Hillig and Mahlberg published a chemotaxomic analysis of cannabinoid variation in their Cannabis germplasm collection. They used gas chromatography to determine cannabinoid content and to infer allele frequencies of the gene that controls CBD and THC production within the studied populations, and concluded that the patterns of cannabinoid variation support recognition of C. sativa and C. indica as separate species, but not C. ruderalis. The authors assigned fiber/seed landraces and feral populations from Europe, central Asia, and Asia Minor to C. sativa. Narrow-leaflet and wide-leaflet drug accessions, southern and eastern Asian hemp accessions, and feral Himalayan populations were assigned to C. indica. In 2005, Hillig published a genetic analysis of the same set of accessions (this paper was the first in the series, but was delayed in publication), and proposed a three-species classification, recognizing C. sativa, C. indica, and (tentatively) C. ruderalis. In his doctoral dissertation published the same year, Hillig stated that principal components analysis of phenotypic (morphological) traits failed to differentiate the putative species, but that canonical variates analysis resulted in a high degree of discrimination of the putative species and infraspecific taxa. Another paper in the series on chemotaxonomic variation in the terpenoid content of the essential oil of Cannabis revealed that several wide-leaflet drug strains in the collection had relatively high levels of certain sesquiterpene alcohols, including guaiol and isomers of eudesmol, that set them apart from the other putative taxa. Hillig concluded that the patterns of genetic, morphological, and chemotaxonomic variation support recognition of C. sativa and C. indica as separate species. He also concluded there is little support to treat C. ruderalis as a separate species from C. sativa at this time, but more research on wild and weedy populations is needed because they were underrepresented in their collection.

In September 2005, New Scientist reported that researchers at the Canberra Institute of Technology had identified a new type of Cannabis based on analysis of mitochondrial and chloroplast DNA. The New Scientist story, which was picked up by many news agencies and web sites, indicated that the research was to be published in the journal Forensic Science International.

Popular usage
The scientific debate regarding taxonomy has had little effect on the terminology in widespread use among cultivators and users of drug-type Cannabis. Cannabis aficionados recognize three distinct types based on such factors as morphology, native range, aroma, and subjective psychoactive characteristics. "Sativa" is the term used to describe the most widespread variety, which is usually tall, laxly branched, and found in warm lowland regions. "Indica" is used to designate shorter, bushier plants adapted to cooler climates and highland environments. "Ruderalis" is the term used to describe the short plants that grow wild in Europe and central Asia.

Breeders, seed companies, and cultivators of drug type Cannabis often describe the ancestry or gross phenotypic characteristics of cultivars by categorizing them as "pure indica," "mostly indica," "indica/sativa," "mostly sativa", or "pure sativa."

One of the most popular and potent sativas in Africa is Malawi Gold, locally known as chamba. It is internationally known for its potency and its flavor.

Breeding systems
Cannabis is predominantly dioecious, although many monoecious varieties have been described. Subdioecy (the occurrence of monoecious individuals and dioecious individuals within the same population) is widespread. Many populations have been described as sexually labile.

As a result of intensive selection in cultivation, Cannabis exhibits many sexual phenotypes that can be described in terms of the ratio of female to male flowers occurring in the individual, or typical in the cultivar. Dioecious varieties are preferred for drug production, where typically the female flowers are used. Dioecious varieties are also preferred for textile fiber production, whereas monoecious varieties are preferred for pulp and paper production. It has been suggested that the presence of monoecy can be used to differentiate licit crops of monoecious hemp from illicit drug crops. However, the so-called "sativa" drug strains often produce monoecious individuals, probably as a result of inbreeding.

Mechanisms of sex determination
Cannabis has been described as having one of the most complicated mechanisms of sex determination among the dioecious plants. Many models have been proposed to explain sex determination in Cannabis.

Based on studies of sex reversal in hemp, it was first reported by K. Hirata in 1924 that an XY sex-determination system is present. At the time, the XY system was the only known system of sex determination. The X:A system was first described in Drosophila spp in 1925. Soon thereafter, Schaffner disputed Hirata's interpretation, and published results from his own studies of sex reversal in hemp, concluding that an X:A system was in use and that furthermore sex was strongly influenced by environmental conditions.

Since then, many different types of sex determination systems have been discovered, particularly in plants. Dioecy is relatively uncommon in the plant kingdom, and a very low percentage of dioecious plant species have been determined to use the XY system. In most cases where the XY system is found it is believed to have evolved recently and independently.

Since the 1920s, a number of sex determination models have been proposed for Cannabis. Ainsworth describes sex determination in the genus as using "an X/autosome dosage type".



The question of whether heteromorphic sex chromosomes are indeed present is most conveniently answered if such chromosomes were clearly visible in a karyotype. Cannabis was one of the first plant species to be karyotyped; however, this was in a period when karyotype preparation was primitive by modern standards (see History of Cytogenetics). Heteromorphic sex chromosomes were reported to occur in staminate individuals of dioecious "Kentucky" hemp, but were not found in pistillate individuals of the same variety. Dioecious "Kentucky" hemp was assumed to use an XY mechanism. Heterosomes were not observed in analyzed individuals of monoecious "Kentucky" hemp, nor in an unidentified German cultivar. These varieties were assumed to have sex chromosome composition XX. According to other researchers, no modern karyotype of Cannabis had been published as of 1996. Proponents of the XY system state that Y chromosome is slightly larger than the X, but difficult to differentiate cytologically.

More recently, Sakamoto and various co-authors have used RAPD to isolate several genetic marker sequences that they name Male-Associated DNA in Cannabis (MADC), and which they interpret as indirect evidence of a male chromosome. Several other research groups have reported identification of male-associated markers using RAPD and AFLP. Ainsworth commented on these findings, stating,"'It is not surprising that male-associated markers are relatively abundant. In dioecious plants where sex chromosomes have not been identified, markers for maleness indicate either the presence of sex chromosomes which have not been distinguished by cytological methods or that the marker is tightly linked to a gene involved in sex determination. '"

Environmental sex determination is known to occur in a variety of species. Many researchers have suggested that sex in Cannabis is determined or strongly influenced by environmental factors. Ainsworth reviews that treatment with auxin and ethylene have feminizing effects, and that treatment with cytokinins and gibberellins have masculinizing effects. It has been reported that sex can be reversed in Cannabis using chemical treatment. A PCR-based method for the detection of female-associated DNA polymorphisms by genotyping has been developed.

Industrial and personal uses
Cannabis is used for a wide variety of purposes.

Hemp
Hemp is the durable soft fiber from the stalk of Cannabis sativa plants. Certain varieties may grow more than six metres tall. Cannabis plants used for hemp production are not suitable for most traditional recreational uses, because such plants produce minimal levels of the major psychoactive compounds (THC in particular). Traditional strains of Cannabis plants cultivated for drug production tend to be difficult to camouflage among hemp plants, because they are visibly different.

Hemp producers sell hemp seeds as a health food, as they are rich in sought-after essential fatty acids and have a good amino acid balance, together with various vitamins and minerals. Hemp "milk" is a milk substitute made from hemp seeds; it is both dairy- and gluten-free.

As a field crop hemp is fairly undemanding and matures more rapidly than most. Horticulturally hemp plants have attractions such as requiring little application of insecticide because they are little attacked; they also do not require much application of herbicides because they grow competitively, with good height, density and foliage. Such characteristics make it easy to grow hemp without excessive environmental impact as long as the application of fertilizer is competently managed. The world's leading producer of hemp is China.

Hemp is valuable in tens of thousands of commercial products, especially as fibre ranging from paper, cordage, construction material and textiles in general, to clothing, in which hemp is stronger and longer-lasting than cotton. It also is a useful source of biofuels (from the oils found in the seeds) and medical products. Hemp has been used by many civilizations, from China to Europe (and later North America) during the last 12,000 years or so. In modern times novel applications and improvements have been explored with modest commercial success.

Recreational use


Cannabis is a popular recreational drug around the world, only behind alcohol, caffeine and tobacco. In the United States alone, it is believed that over 100 million Americans have tried Cannabis, with 25 million Americans having used it within the past year.

The psychoactive effects of Cannabis are known to have a biphasic nature. Primary psychoactive effects include a state of relaxation, and to a lesser degree, euphoria from its main psychoactive compound, tetrahydrocannabinol. Secondary psychoactive effects, such as a facility for philosophical thinking, introspection and metacognition have been reported amongst cases of anxiety and paranoia. Finally, the tertiary psychoactive effects of the drug cannabis, can include an increase in heart rate and hunger, believed to be caused by 11-Hydroxy-THC, a psychoactive metabolite of THC produced in the liver.

Normal cognition is restored after approximately three hours for larger doses via a smoking pipe, bong or vaporizer. However, if a large amount is taken orally the effects may last much longer. After 24 hours to a few days, minuscule psychoactive effects may be felt, depending on dosage, frequency and tolerance to the drug.



Various forms of the drug cannabis exist, including extracts such as hashish and hash oil which, because of appearance, are more susceptible to adulterants when left unregulated.

The plant Cannabis sativa is known to cause more of a "high" by stimulating hunger and by producing a rather more comedic, or energetic feeling. Conversely, the Cannabis indica plant is known to cause more of a "stoned" or meditative feeling, possibly because of a higher CBD to THC ratio.

Cannabidiol (CBD), which has no psychotropic effects by itself (although sometimes showing a small stimulant effect, similar to caffeine), attenuates, or reduces the higher anxiety levels caused by THC alone.

According to the UK medical journal The Lancet, Cannabis has a lower rate of dependence compared to both nicotine and alcohol. However, everyday use of Cannabis can in some cases be correlated with psychological withdrawal symptoms such as irritability and insomnia, and evidence could suggest that if a user experiences stress, the likeliness of getting a panic attack increases because of an increase of THC metabolites. However, Cannabis withdrawal symptoms are typically mild and are never life-threatening.

Medical use
A synthetic form of the main psychoactive cannabinoid in Cannabis, Δ9-tetrahydrocannabinol (THC), is used as a treatment for a wide range of medical conditions.

In the United States, although the Food and Drug Administration (FDA) does acknowledge that "there has been considerable interest in its use for the treatment of a number of conditions, including glaucoma, AIDS wasting, neuropathic pain, treatment of spasticity associated with multiple sclerosis, and chemotherapy-induced nausea," the agency has not approved "medical marijuana". There are currently 2 oral forms of cannabis (cannabinoids) available by prescription in the United States for nausea and vomiting associated with cancer chemotherapy: dronabinol (Marinol) and nabilone (Cesamet). Dronabinol is also approved for the treatment of anorexia associated with AIDS. The FDA does facilitate scientific investigations into the medical uses of cannabinoids.

In a collection of writings on medical marijuana by 45 researchers, a literature review on the medicinal uses of Cannabis and cannabinoids concluded that established uses include easing of nausea and vomiting, anorexia, and weight loss; "well-confirmed effect" was found in the treatment of spasticity, painful conditions (i.e. neurogenic pain), movement disorders, asthma, and glaucoma. Reported but "less-confirmed" effects included treatment of allergies, inflammation, infection, epilepsy, depression, bipolar disorders, anxiety disorder, dependency and withdrawal. Basic level research was being carried out at the time on autoimmune disease, cancer, neuroprotection, fever, and disorders of blood pressure.

Clinical trials conducted by the American Marijuana Policy Project, have shown the efficacy of cannabis as a treatment for cancer and AIDS patients, who often suffer from clinical depression, and from nausea and resulting weight loss due to chemotherapy and other aggressive treatments. A synthetic version of the cannabinoid THC named dronabinol has been shown to relieve symptoms of anorexia and reduce agitation in elderly Alzheimer's patients. Dronabinol has been approved for use with anorexia in patients with HIV/AIDS and chemotherapy-related nausea. This drug, while demonstrating the effectiveness of Cannabis at combating several disorders, is more expensive and less available than whole cannabis and has not been shown to be effective or safe.

Glaucoma, a condition of increased pressure within the eyeball causing gradual loss of sight, can be treated with medical marijuana to decrease this intraocular pressure. There has been debate for 25 years on the subject. Some studies have shown a reduction of IOP in glaucoma patients who smoke cannabis, but the effects are generally short-lived. There exists some concern over its use since it can also decrease blood flow to the optic nerve. Marijuana lowers IOP by acting on a cannabinoid receptor on the ciliary body called the CB receptor. Although Cannabis may not be the best therapeutic choice for glaucoma patients, it may lead researchers to more effective treatments. A promising study shows that agents targeted to ocular CB receptors can reduce IOP in glaucoma patients who have failed other therapies.

Medical cannabis is also used for analgesia, or pain relief. It is also reported to be beneficial for treating certain neurological illnesses such as epilepsy, and bipolar disorder. Case reports have found that Cannabis can relieve tics in people with obsessive compulsive disorder and Tourette syndrome. Patients treated with tetrahydrocannabinol, the main psychoactive chemical found in Cannabis, reported a significant decrease in both motor and vocal tics, some of 50% or more. Some decrease in obsessive-compulsive behavior was also found. A recent study has also concluded that cannabinoids found in Cannabis might have the ability to prevent Alzheimer's disease. THC has been shown to reduce arterial blockages.

Another potential use for medical cannabis is movement disorders. Cannabis is frequently reported to reduce the muscle spasms associated with multiple sclerosis; this has been acknowledged by the Institute of Medicine, but it noted that these abundant anecdotal reports are not well-supported by clinical data. Evidence from animal studies suggests that there is a possible role for cannabinoids in the treatment of certain types of epileptic seizures. A synthetic version of the major active compound in Cannabis, THC, is available in capsule form as the prescription drug dronabinol (Marinol) in many countries. The prescription drug Sativex, an extract of cannabis administered as a sublingual spray, has been approved in Canada for the treatment of multiple sclerosis.

Cannabis was manufactured and sold by U.S. pharmaceutical companies from the 1880s through the 1930s, but the lack of documented information on the frequency and effectiveness of its use makes it difficult to evaluate its medicinal value in these forms. Cannabis was listed in the 1929–1930 Physicians' Catalog of the Pharmaceutical and Biological Products of Parke, Davis & Company as an active ingredient in ten products for cough, colic, neuralgia, cholera mordus and other medical conditions, as well as a "narcotic, analgesic, and sedative." The 1929–1930 Physicians' Catalog also lists compound medications containing cannabis that in some cases were apparently formulated by medical doctors, in its "Pills and Tablets" section.

As cannabis is further legalized for medicinal use, it is possible that some of the foregoing compound medicines, whose formulas have been copied exactly as published, may be scientifically tested to determine whether they are effective medications. Writing in the Canadian Medical Association Journal, smoking cannabis from a pipe may significantly relieve chronic pain in patients with damaged nerves. A study on New Zealand support the claim that that long-term cannabis smoking increases the risk of lung cancer in young adults.

Cannabis sativa
Jack Herer, a sativa-dominant strain, is effective in relieving anxiety, nervousness, stress and depression. It is also viewed as a motivational medicine, stimulating energy, creativity and concentration.

Ancient and religious uses
The Yanghai Tombs, a vast ancient cemetery (54 000 m2) situated in the Turfan district of the Xinjiang Uyghur Autonomous Region of the People's Republic of China, have revealed the 2700-year-old grave of a shaman. He is thought to have belonged to the Jushi culture recorded in the area centuries later in the Hanshu, Chap 96B. Near the head and foot of the shaman was a large leather basket and wooden bowl filled with 789g of cannabis, superbly preserved by climatic and burial conditions. An international team demonstrated that this material contained tetrahydrocannabinol, the psychoactive component of cannabis. The cannabis was presumably employed by this culture as a medicinal or psychoactive agent, or an aid to divination. This is the oldest documentation of cannabis as a pharmacologically active agent.

Settlements which date from c. 2200-1700 BCE in the Bactria and Margiana contained elaborate ritual structures with rooms containing everything needed for making drinks containing extracts from poppy (opium), hemp (cannabis), and ephedra (which contains ephedrine). "'While we have no evidence of the use of ephedra among the steppe tribes, we have already seen that they did share in the cultic use of hemp, a practice that ranged from Romania east to the Yenisei River from at least the 3rd millenium BC onwards where its use was later encountered in the apparatus for smoking hemp found at Pazyryk.'"

Cannabis is first referred to in Hindu Vedas between 2000 and 1400 BCE, in the Atharvaveda. By the 10th century CE, it has been suggested that it was referred to by some in India as "food of the gods". Cannabis use eventually became a ritual part of the Hindu festival of Holi.

In Buddhism, cannabis is generally regarded as an intoxicant and therefore a hindrance to development of meditation and clear awareness. In ancient Germanic culture, Cannabis was associated with the Norse love goddess, Freya. An anointing oil mentioned in Exodus is, by some translators, said to contain Cannabis. Sufis have used Cannabis in a spiritual context since the 13th century CE.

In the Punjab, Cannabis or Sukha ( ਸੁੱਖਾ ਪ੍ਰਰਸਾਦ ), "peace-giver", is the term Sikhs use to refer to it. Initiated by the tenth guru of the Sikhs, Guru Gobind Singh, cannabis or bhang (ਭੰਗ) was used to help in meditation and was also used before battles to aid as a painkiller, growing naturally all over Punjab. Narrated by many historical and native accounts cannabis is pounded by the Sikhs, especially during religious festivals like Hola Mohalla.[43] Even today, Nihang Sikhs gather in their thousands at Anandpur, on the occasion of the festival of Hola Mohalla and display their martial skills and of course cannabis is pounded by the Nihang Sikhs. This tradition has been in place since the time of Guru Gobind Singh. Their fighting style is referred to as shastar vidiya, which is among the most intimidating and brutal martial art. The compositions from the Sri Dasam Granth are used in unison with the battle maneuvers.

In modern times the Rastafari movement has embraced Cannabis as a sacrament. Elders of the Ethiopian Zion Coptic Church, a religious movement founded in the United States in 1975 with no ties to either Ethiopia or the Coptic Church, consider Cannabis to be the Eucharist, claiming it as an oral tradition from Ethiopia dating back to the time of Christ. Like the Rastafari, some modern Gnostic Christian sects have asserted that Cannabis is the Tree of Life. Other organized religions founded in the 20th century that treat Cannabis as a sacrament are the THC Ministry, the Way of Infinite Harmony, Cantheism, the Cannabis Assembly and the Church of Cognizance.

Rastafari and Sikh use tend to be among the biggest consumers of modern Cannabis use.

Aspects of cannabis production and use

 * Cannabis cultivation discusses aspects of cultivation for medicinal and recreational drug purposes.
 * Cannabis (drug) discusses its use as a recreational drug.
 * Health issues and the effects of cannabis discusses the pharmacology, physical, and mental effects of Cannabis when used as drug.
 * Hemp discusses its uses as a source of housing, oil, food, fibers, and industrial materials.
 * Legality of cannabis focuses on the law and enforcement aspects of growing, transporting, selling and using Cannabis as a drug.
 * Cannabis reclassification in the United Kingdom.
 * Cannabis rescheduling in the United States.
 * Drug policy of the Netherlands.
 * Medical Cannabis discusses its use as a medication.
 * Spiritual use of cannabis discusses sacramental and religious use.