Various strains of "medical marijuana" are found to have a significant variation in the ratios of CBD-to-THC, and are known to contain other non-psychotropic cannabinoids.[60] Any psychoactive marijuana, regardless of its CBD content, is derived from the flower (or bud) of the genus Cannabis. Non-psychoactive hemp (also commonly-termed industrial hemp), regardless of its CBD content, is any part of the cannabis plant, whether growing or not, containing a ∆-9 tetrahydrocannabinol concentration of no more than 0.3% on a dry-weight basis.[61] Certain standards are required for legal growing, cultivating, and producing the hemp plant. The Colorado Industrial Hemp Program registers growers of industrial hemp and samples crops to verify that the dry-weight THC concentration does not exceed 0.3%.[61]
CBD’s therapeutic potential with respect to addiction also extends to the serotonin system. Animal studies have demonstrated that CBD directly activates multiple serotonin receptors in the brain. These interactions have been implicated in its ability to reduce drug-seeking behavior. CBD’s influence on the serotonin system may also account in part for its anti-anxiety properties, which have been robustly demonstrated across both human and animal studies.
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.[32] According to other researchers, no modern karyotype of Cannabis had been published as of 1996.[33] Proponents of the XY system state that Y chromosome is slightly larger than the X, but difficult to differentiate cytologically.[34]
^ Jump up to: a b Schreiner AM, Dunn ME (October 2012). "Residual effects of cannabis use on neurocognitive performance after prolonged abstinence: a meta-analysis". Experimental and Clinical Psychopharmacology. 20 (5): 420–429. doi:10.1037/a0029117. PMID 22731735. Therefore, results indicate evidence for small neurocognitive effects that persist after the period of acute intoxication...As hypothesized, the meta-analysis conducted on studies eval- uating users after at least 25 days of abstention found no residual effects on cognitive performance...These results fail to support the idea that heavy cannabis use may result in long-term, persistent effects on neuropsychological functioning.
Because of its cloudy classification and constantly-shifting political winds, CBD creates a legal quagmire for anybody who wants to study or recommend its effectiveness as a medicine for animals. To date, there have been no rigorous scientific studies published on marijuana, or even the non-psychoactive CBD, as a treatment for pets with arthritis, seizures, anxiety, or any other medical conditions. But that may soon (hopefully) be changing, as a few studies are either in the planning stages or underway. 
The genus Cannabis was first classified using the "modern" system of taxonomic nomenclature by Carl Linnaeus in 1753, who devised the system still in use for the naming of species.[60] 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.[61] 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.[62] 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.[63]
Cannabidiol (CBD) is a naturally occurring compound found in the resinous flower of cannabis, a plant with a rich history as a medicine going back thousands of years. Today the therapeutic properties of CBD are being tested and confirmed by scientists and doctors around the world. A safe, non-addictive substance, CBD is one of more than a hundred “phytocannabinoids,” which are unique to cannabis and endow the plant with its robust therapeutic profile.
Cannabis use has the hallmark pathologic features shared by all substance use disorders. Like other drugs of abuse, Cannabis causes compulsive drug-seeking behaviors, loss of self-control, withdrawal symptoms, and the propensity to relapse.57 Cannabis use disorder has been recognized as a bona fide disorder and has been included in the most recent version of the Diagnostic and Statistical Manual of Mental Disorders (fifth edition).58 Long-term clinical outcomes for Cannabis use disorder may be less severe than for other drugs of abuse but the addictive processes appears to be very similar. Animal models of addiction have clearly supported the notion that Cannabis has addictive properties.

• What's the dosing? This is a confusing one for many people. "A lot of brands don't do a good job of clearly instructing their consumer on the dosing," says Chris Roth, CEO and co-founder of Highline Wellness. When thinking about dosing, also consider whether your CBD is full-spectrum or isolate: Full-spectrum could include other cannabinoids like cannabidivarin or cannabigerol (this is important, since "there's something called the 'entourage effect' when all together, they're more effective than any one of them alone," Roth explains), while isolate is 100% CBD. "Some people might only need 10 milligrams of full-spectrum CBD, but with isolate, even taking 80 or 100 milligrams might not have the same effect," he says.
^ Blest-Hopley G, Giampietro V, Bhattacharyya S (May 2018). "Residual effects of cannabis use in adolescent and adult brains - A meta-analysis of fMRI studies". Neuroscience and Biobehavioral Reviews. 88: 26–41. doi:10.1016/j.neubiorev.2018.03.008. PMID 29535069. This may reflect the multitude of cognitive tasks employed by the various studies included in these meta-analyses, all of which involved performing a task thereby requiring the participant to reorient their attention and attempt to solve the problem at hand and suggest that greater engagement of this region indicates less efficient cognitive performance in cannabis users in general, irrespective of their age.

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