There is reasonable evidence from prospective epidemiological studies which suggests that cannabis use can precipitate schizophrenia in persons who are vulnerable because of a personal or family history of schizophrenia. There is also evidence that a genetic vulnerability to psychosis increases the risk that cannabis users will develop psychosis (McGuire et al., 1995; Arseneault et al., 2002; Verdoux et al., 2002). A casual relationship also has biological plausibility in that the cannabinoid and dopaminergic neurotransmitter systems interact in animals. D'Souza and colleagues (1999) have shown in a provocation study that THC produces a dose-dependent increase in psychotic symptoms under double-blind placebo conditions; and Caspi and colleagues (2005) have shown an interaction between specific alleles of the COMT allele and psychotogenic effects of cannabis. If these results can be replicated and extended, they will increase the likelihood that cannabis can be a contributory cause of psychosis in vulnerable individuals.
By the 1930s, marijuana was banned in 24 states. The newly minted Federal Bureau of Narcotics launched a campaign against the drug, and newspapers fueled hysteria with headlines like the 1933 Los Angeles Examiner's "Murder Weed Found Up and Down the Coast — Deadly Marihuana Dope Plant Ready for Harvest That Means Enslavement of California Children." By 1937, Congress passed the Marihuana Tax Act, which effectively banned marijuana except for a few medicinal purposes, according to "Smoke Signals: A Social History of Marijuana – Medical, Recreational and Legal" (Scribner, 2012).

In December 2012, the U.S. state of Washington became the first state to officially legalize cannabis in a state law (Washington Initiative 502) (but still illegal by federal law),[227] with the state of Colorado following close behind (Colorado Amendment 64).[228] On January 1, 2013, the first marijuana "club" for private marijuana smoking (no buying or selling, however) was allowed for the first time in Colorado.[229] The California Supreme Court decided in May 2013 that local governments can ban medical marijuana dispensaries despite a state law in California that permits the use of cannabis for medical purposes. At least 180 cities across California have enacted bans in recent years.[230]
First the unsatisfying answer: Vets don’t have anything definitive to say about marijuana or CBD products for dogs because, as mentioned above, they have limited means to study the potential benefits and, more importantly, the potential for harm. At best, you might find a vet who will say that CBD probably won’t be harmful to dogs, and it may or may not offer any actual benefit. 

Like any medications, overdosing can lead to potential risks for pets. “The most significant is THC toxicity, meaning, essentially, they are high,” Richter says. “Depending on how significantly a pet has been overdosed, the effects of that can be quite long-lasting, even days.” During these episodes, a pet may not be able to stand or eat. If you suspect an overdose, take your pet to the veterinarian immediately.
Fig. 25. The “hemp house” under construction on the Oglala Lakota Nation (Pine Ridge Reservation), South Dakota. Foundation blocks for the house are made with hemp fiber as a binder in cement. Stucco is also of hemp. Shingles are 60% hemp in a synthetic polymer. Hemp insulation is used throughout. (Courtesy of Oglala Sioux Tribe, Slim Butte Land Use Association, and S. Sauser.)
The reason researchers and cannabis companies are interested in alternative ways of producing cannabinoids is that working with the original plant is messy and complicated. First of all, growing the stuff takes a lot of time, water, and energy (if you’re cultivating indoors). Extracting certain cannabinoids from flower is also a hassle. If you’re only after CBD, for example, there’s a chance your extract could be contaminated with THC. This is of particular concern if you want to isolate CBD for use as a medicine—it’s been shown, for instance, to be remarkably effective in treating epilepsy.
Hemp rope was used in the age of sailing ships, though the rope had to be protected by tarring, since hemp rope has a propensity for breaking from rot, as the capillary effect of the rope-woven fibers tended to hold liquid at the interior, while seeming dry from the outside.[44] Tarring was a labor-intensive process, and earned sailors the nickname "Jack Tar". Hemp rope was phased out when manila rope, which does not require tarring, became widely available. Manila is sometimes referred to as Manila hemp, but is not related to hemp; it is abacá, a species of banana.
According to DSM-V criteria, 9% of those who are exposed to cannabis develop cannabis use disorder, compared to 20% for cocaine, 23% for alcohol and 68% for nicotine. Cannabis abuse disorder in the DSM-V involves a combination of DSM-IV criteria for cannabis abuse and dependence, plus the addition of craving, minus the criterion related to legal troubles.[117]
The objectivity of scientific evaluation of the medicinal value of marijuana to date has been questioned. In the words of Hirst et al. (1998): “The ...status of cannabis has made modern clinical research almost impossible. This is primarily because of the legal, ethical and bureaucratic difficulties in conducting trials with patients. Additionally, the general attitude towards cannabis, in which it is seen only as a drug of abuse and addiction, has not helped.” In a recent editorial, the respected journal Nature (2001) stated: “Governments, including the US federal government, have until recently refused to sanction the medical use of marijuana, and have also done what they can to prevent its clinical testing. They have defended their inaction by claiming that either step would signal to the public a softening of the so-called ‘war on drugs.’... The pharmacology of cannabinoids is a valid field of scientific investigation. Pharmacologists have the tools and the methodologies to realize its considerable potential, provided the political climate permits them to do so.” Given these current demands for research on medicinal marijuana, it will be necessary to produce crops of drug types of C. sativa.
Cannabis sativa is an annual wind-pollinated plant, normally dioecious and dimorphic, although sometimes monoecious (mostly in several modern European fiber cultivars). Figure 2 presents the basic morphology of the species. Some special hybrids, obtained by pollinating females of dioecious lines with pollen from monoecious plants, are predominantly female (so-called “all-female,” these generally also produce some hermaphrodites and occasional males). All-female lines are productive for some purposes (e.g. they are very uniform, and with very few males to take up space they can produce considerable grain), but the hybrid seed is expensive to produce. Staminate or “male” plants tend to be 10%–15% taller and are less robust than the pistillate or “female” (note the comparatively frail male in Fig. 3). So prolific is pollen production that an isolation distance of about 5 km is usually recommended for generating pure-bred foundation seed. A “perigonal bract” subtends each female flower, and grows to envelop the fruit. While small, secretory, resin-producing glands occur on the epidermis of most of the above-ground parts of the plant, the glands are very dense and productive on the perigonal bracts, which are accordingly of central interest in marijuana varieties. The root is a laterally branched taproot, generally 30–60 cm deep, up to 2.5 m in loose soils, very near the surface and more branched in wet soils. Extensive root systems are key to the ability of hemp crops to exploit deep supplies of nutrients and water. The stems are erect, furrowed, and usually branched, with a woody interior, and may be hollow in the internodes. Although the stem is often woody, the species is frequently referred to as a herb or forb. Plants vary enormously in height depending on genetic constitution and environment (Fig. 4), but are typically 1–5 m (heights of 12 m or more in cultivation have been claimed).

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