IACM-Bulletin of November 23, 2008

Science — Why cannabis smokers may have a lower cancer risk than tobacco smokers

Eleven scientists from the USA and Taiwan summarized data from basic research and a re-evaluation of an epidemiological study by Sidney and colleagues from 1997. Their investigation indicates that cannabis smoke may not increase or even decrease the incidence of cancers associated with tobacco smoke. While cannabis smoke contains higher levels of carcinogenic polycyclic aromatic hydrocarbons (PAH) than in tobacco smoke, this may not mean that cannabis smokers are at a higher cancer risk than tobacco smokers, since the level of PAHs is less important than the influence of substances on PAH activation by certain enzymes in the liver. "Not surprisingly, spiking tobacco tar with delta-9-THC markedly reduced carcinogenic activity" in experiments with cancer cells, scientists wrote in an article for the Journal of Psychoactive Drugs.

It is known that cannabis smoking causes precursors of cancer, which are also observed in tobacco smokers. However, studies show that these precursors "may have little, if any predictive value" and these lesions are "generally reversible and often regress spontaneously." In studies with monkeys "prolonged exposure to marijuana smoke failed to produce any carcinogenic effects."

In the cohort study by Sidney et al. (1997) with about 65,000 subjects tobacco smokers had a significantly higher risk to develop lung cancer than cannabis smokers after a mean observation period of 8.6 years. In addition, cannabis smokers had a significantly lower lung cancer risk than subjects, who did not smoke cannabis. In reply to the argument, Sidney and colleagues did not follow the participants of their study long enough to find an increased incidence of cancers in the cannabis group, they noted that "surprising enough, the follow-up period was sufficient to observe 179 cases of TRC [tobacco related cancers] (including lung) among TS [tobacco smokers]." If the cancer risk of tobacco smokers equals that of non-smokers, then 130 cases would be expected among tobacco smokers. In contrast, only three cases of tobacco related cancers were observed in cannabis smokers. If the incidence of tobacco related cancers in cannabis smokers equals that of non-smokers, "then 16 cases would be expected in MS [marijuana smokers]."

(Source: Chen AL, Chen TJ, Braverman ER, Acuri V, Kemer M, Varshavskiy M, Braverman D, Downs WB, Blum SH, Cassel K, Blum K. Hypothesizing that marijuana smokers are at a significantly lower risk of carcinogenicity relative to tobacco-non-marijuana smokers: evidenced based on statistical reevaluation of current literature. J Psychoactive Drugs 2008;40(3):263-72.)

News in brief

USA — New Mexico

Since medicinal cannabis was legalized in New Mexico in 2007, there are about 200 medical cannabis users in the state, according to the Drug Policy Alliance. However, patients have no place to legally purchase the drug. (Source: Daily Lobo of 13 November 2008)

Science — Tobacco and THC

According to research at the University of Leiden, the Netherlands, mixing cannabis with tobacco increased the amount of THC inhaled per gram of cannabis from a mean of 33 mg/g for a cigarette only containing cannabis to 59 mg/g for a cigarette containing 25 per cent cannabis and 75 per cent tobacco. (Source: Van der Kooy F, et al. Inhal Toxicol. 2008 Oct 14:1. [Electronic publication ahead of print])

The possession of a small amount of cannabis for personal use would be punished far less strictly than that of other drugs, according to a change of the law by the lower house of parliament on 11 November. While the production and sale of drugs can be punished with five to 15 years in prison, if people have a small amount of cannabis on them it is only an offence, under the new law. It is yet to be discussed by the upper house and signed by the president into law. (Source: Ceske noviny of 11 November 2008)

Holland — Mayors

A majority of Dutch mayors (54 out of 88), who have a coffee shop in their city, support the legalisation of the entire cannabis production chain. They want to end the frontdoor-backdoor problem, where sales of cannabis is legal but growing is not. (Source: Psychonaut.com of 19 November 2008)

Science — Psychosis

According to British researchers the use of cannabis causes increased experiences of delusions and hallucinations in individuals prone to psychosis. Their findings suggest that an individual's response to acute cannabis consumption may be a marker of occurrence of harmful psychic effects of cannabis. (Source: Mason O, et al. Psychol Med. 2008 Nov 19:1-6. [Electronic publication ahead of print])

Science — Cannabis dependence

A study conducted in the USA with 1.923 subjects shows that certain variations of the DNA sequence of the gene for the cannabinoid-1 receptor may be associated with an increased risk for cannabis dependence. (Source: Agrawal A, et al. Am J Med Genet B Neuropsychiatr Genet. 2008 Nov 14. [Electronic publication ahead of print])

Science — Schizophrenia

According to research at the Psychiatric University Hospital Zurich, Switzerland, on the reasons for cannabis use patients with schizophrenia more often than healthy controls stated that they consumed cannabis to fight boredom and to ease social contacts. (Source: Schaub M, et al. Aust N Z J Psychiatry 2008;42(12):1060-5.)

Science — Pain

Scientists from the University of Bonn, Germany, demonstrated that the CB2 receptor in cells of the immune system is involved in the development of neuropathic pain. The CB2 receptor was important for the modulation of the activation of glia cells in response to nerve injury. (Source: Racz I, et al. J Neurosci 2008;28(46):12125-35.)

Science — Food intake

Animal research shows that CB2 receptor ligands, i.e. substances that bind to the CB2 receptor, may play a role in food and alcohol consumption. (Source: Onaivi ES, et al. Ann N Y Acad Sci 2008;1139:426-33.)

UK — Poll on illegal drugs

According to a poll conducted for the Observer and the Guardian newspapers 27 per cent of UK adults have taken illegal drugs and 87 per cent of these have taken cannabis. 32 per cent believe that drug laws in the UK are too liberal, 50 per cent think that they are about right and 18 per cent believe that they are not liberal enough. 27 per cent of responders said that certain drugs should be legalized or decriminalized. A sample of 1,008 UK adults aged 16 years or older were interviewed by ICM Research in October 2008. (Source: The Observer of 16 November 2008)