In the first decades of the 20th century, the Western medical use of cannabis significantly decreased. This may have occurred, among other factors, because of the difficulty to obtain replicable effects, due to the extreme varying efficacy of different samples of the plant. At that time, the active principle of cannabis had not yet been isolated and the drug was used in the form of tinctures or extracts whose power was dependent on different factors, such as origin, age, and mode of preparation.8 In addition, various medications appeared at the end of the 19th century, with known efficacy for the treatment of the main indications of cannabis. Vaccines were developed for various infectious diseases, such as tetanus; effective analgesics such as aspirin appeared , and hypodermic syringes allowed the injectable use of morphine; and, as a narcotic and sedative, cannabis was rivaled by substances such as chloral hydrate, paraldehyde, and barbiturates.8
Finally, many legal restrictions limited the medical use and experimentation of cannabis. In the United States, as the result of a campaign of the Federal Bureau of Narcotics, the Marihuana Tax Act law was passed in 1937. Under this Act, anyone using the plant was required to register and pay a tax of a dollar an ounce (28.35 g), for medical purposes, and 100 dollars an ounce for any other use. Despite the low value for medical use, the non-payment of this tax, however, resulted in a 2.000 dollar fine and/or 5 years imprisonment. This law brought difficulties for the use of the plant due to the excessive paperwork and the risk of severe punishment. When cannabis transaction regulations, including prescriptions, were transferred to the tribute area, this law circumvented a decision of the Supreme Court which gave the States the right to control commercial transactions and, in practice, meant banning the use of cannabis in the whole American territory. Cannabis was removed from the American pharmacopoeia in 1941.6,14
In the second half of the 20th century, cannabis reached great social importance due to the explosion of its consumption for hedonistic purposes. Until that time, in the West, the hedonistic use of the plant was limited to small groups. In Europe, groups of intellectuals gathered to use the drug. Descriptions of this use may be found in novels by 20th century French writers, such as Gautier and Boudelaire. In the Americas, this practice was relatively common among the Black in the rural area of Northeastern Brazil since the 16th century, who would meet on weekends to use the drug in groups. This use was later passed on to fishermen of the San Francisco River and by sea to the coastal cities. In the early 20th century, the use of cannabis in Brazil remained restricted to small low-socioeconomic groups, and was known as the 'opium of the poor'.10 In Mexico, cannabis was also used by the most underprivileged population and it was through Mexican immigrants that its use, for recreation, reached the United States in the first decades of the 20th century. Until the 1950's, in the United States, cannabis use was restricted to the neighborhoods of Blacks and Hispanic immigrants.15
Since the 1960's, the recreational use of cannabis rapidly spread among the younger ranges of the population throughout the Western world. In the United States, the percentage of young adults that had used cannabis, at least once, went from 5%, in 1967, to 44%, 49%, 68%, and 64%, in 1971, 1975, 1980, and 1982, respectively.16-17 This use remains high until today.18-19 In 1964, the chemical structure of D9-THC was identified by Gaoni and Mechoulam,20 which contributed to a proliferation of studies about the active constituents of cannabis.21
The startling boost in cannabis consumption, which intensified its social importance, along with the better knowledge of its chemical composition (which made it possible to obtain its pure constituents) contributed to a significant increase in scientific interest for cannabis, as of 1965. The number of publications about cannabis reached their peak in the early 1970's. In this period, a Brazilian research group, led by Carlini, had a great contribution, especially about the interactions of D9-THC with other cannabinoids.22 Since then, Carlini has been developing efforts for the realignment of public policies concerning cannabis control.23 After the middle of 1970's, the number of publications started to slowly decline during the following two decades. The interest in studies about cannabis was renewed in the early 1990's, with the description and cloning of specific receptors for the cannabinoids in the nervous system and the subsequent isolation of anandamide, an endogenous cannabinoid.24 Afterwards, the number of publications about cannabis has been continuously growing, attesting the great interest in research involving the herb. Figure 2 shows the evolution of the number of publications about cannabis in the last 50 years.
With the growth of scientific interest for cannabis, its therapeutic effects are being once again studied, this time using more accurate scientific methods. There are studies, in different phases, about the therapeutic effects of D9-THC in conditions such as: epilepsy, insomnia, vomits, spasms, pain, glaucoma, asthma, inappetence, Tourette syndrome, and others. Among the therapeutic indications of D9-THC the following are considered close to being proven: anti-emetic, stimulant of appetite, analgesic, and in symptoms of Multiple Sclerosis.25 Other cannabinoids are also under investigation, such as Canabidiol (CBD), which has evidence for therapeutic effects in epilepsy, insomnia, anxiety, inflammations, brain damage (as a neuroprotector), psychoses, and others.26-27 However, cannabis products must be used cautiously since some studies suggest that early-onset cannabis use can induce cognitive deficits and apparently acts as a risk factor for the onset of psychosis among vulnerable youths.28-29
At the beginning of 2005, a multinational pharmaceutical laboratory received the approval in Canada, and is pleading authorization in the United Kingdom and the European Union, to market a medication containing D9-THC and CBD for the relief of neuropathic pain in patients with multiple sclerosis.
Thus, a new cycle begins for the use of cannabis derivatives as medication, this time more consistently than in the past. The structures of chemical compounds derived from cannabis are now known, the mechanisms of their action in the nervous system are being elucidated with the discovery of an endogenous cannabinoid system, and treatment effectiveness and safety are being scientifically proven.
Answers to all your Biology Questions
