Strains of cannabis sativa and cannabis indica possess relatively few significant genetic differences and are often mislabeled by breeders, according to an evaluation of marijuana taxonomy published online last week in the journal PLOS ONE.
Investigators from the University of Manitoba, the University of British Columbia, and Dalhousie University in Nova Scotia evaluated the genetic structure of a diverse range of commonly cultivated marijuana and industrial hemp samples.
Researchers reported, “We find a moderate correlation between the genetic structure of marijuana strains and their reported C. sativa and C. indica ancestry and show that marijuana strain names often do not reflect a meaningful genetic identity.” They added, “This observation suggests that C. sativa and C. indica may represent distinguishable pools of genetic diversity, but that breeding has resulted in considerable admixture between the two. … Our results suggest that the reported ancestry of some of the most common marijuana strains only partially captures their true ancestry.”
By contrast, authors determined, “[M]arijuana and hemp are significantly differentiated at a genome-wide level, demonstrating that the distinction between these populations is not limited to genes underlying THC production. … [This] difference between marijuana and hemp plants has considerable legal implications in many countries.”
In the United States, federal law makes no legal distinction between hemp and cannabis.
Authors concluded: “Achieving a practical, accurate and reliable classification system for cannabis, including a variety registration system for marijuana-type plants, will require significant scientific investment and a legal framework that accepts both licit and illicit forms of this plant. Such a system is essential in order to realize the enormous potential of Cannabis as a multi-use crop (hemp) and as a medicinal plant (marijuana).”
Full text of the study, “The genetic structure of marijuana and hemp,” appears online here.
Two new studies published online today in JAMA (Journal of the American Medical Association) Psychiatry provide little support for previous claims that cannabis exposure is significantly harmful to the developing brain.
The first study, which assessed the effects of cannabis exposure on brain volume in exposed and unexposed sibling pairs, reported that any identifiable differences “were attributable to common predispositional factors, genetic or environmental in origin.” By contrast, authors found “no evidence for the causal influence of cannabis exposure” on brain morphology.
The trial is “the largest study to date examining the association between cannabis exposure (ever versus never used) and brain volumes.”
The study is one of two recent clinical trials to be published in recent months rebutting the claims of a widely publicized 2014 paper which alleged that even casual marijuana exposure may be linked to brain abnormalities, particularly in the region of the brain known as the amygdala. In January, researchers writing in The Journal of Neuroscience reported “no statistically significant differences … between daily [marijuana] users and nonusers on [brain] volume or shape in the regions of interest” after researchers controlled for participants’ use of alcohol. Similarly, today’s JAMA study “casts considerable doubt on hypotheses that cannabis use … causes reductions in amygdala volumes.”
A second study appearing today in the journal assessed whether cannabis use during adolescence is associated with brain changes that may be linked to an increased risk of schizophrenia. While researchers reported finding an association among male subjects who possessed a high genetic predisposition toward schizophrenia, authors reported that no such association existed among male subjects who were at low risk for the disease, or among females in either the high risk or low risk categories. The finding is consistent with the theory that early onset cannabis use may potentially exacerbate symptoms in a minority of subjects predisposed to the disease, but it contradicts claims that marijuana exposure is a likely cause of schizophrenia, particularly among those who are not already vulnerable to the disease.
Abstracts of both new studies appear online in JAMA Psychiatry here and here.
Inhaling cannabis is associated with the remission of refractory idiopathic angioedema, according to a clinical report published in the journal Case Reports in Immunology. Angioedema is a condition characterized by rapid swelling under the skin in regions around the face and throat, which may result in airway obstruction or suffocation.
Investigators from the Soroka University Medical Center in Israel reported on the progress of a 27-year-old male patient with life-threatening, recurrent angioedema of unknown origin. Doctors placed the patient on a regiment of 20 grams of inhaled cannabis monthly after he failed to respond favorably to prescribed steroids and antihistamines.
Authors reported: “The use of inhaled cannabis resulted in a complete response, and he has been free of symptoms for 2 years. An attempt to withhold the inhaled cannabis led to a recurrent attack within a week, and resuming cannabis maintained the remission, suggesting a cause and effect relationship.”
They concluded: “This is the first report in which a cannabis product for the treatment of refractory idiopathic angioedema was associated with an excellent clinical response. … More research into the exact mechanism of action of cannabis products in cases of idiopathic angioedema and on the modulation of the immune response in general is indicated.”
The Israeli government has authorized the limited production and distribution of marijuana as a medical treatment since 2011, and preparations of the plant are expected to be available in pharmacies imminently.
Full text of the report, “Life threatening idiopathic recurrent angioedema responding to cannabis,” appears online here.
A history of cannabis use is associated with a lower likelihood of obesity and diabetes, according to population-based data published in the journal Obesity.
Investigators from the Conference of Quebec University Health Centers assessed cannabis use patterns and body mass index (BMI) in a cohort of 786 Inuit (Arctic aboriginal) adults ages 18 to 74. Researchers reported that subjects who consumed cannabis in the past year were more likely to possess a lower BMI, lower fasting insulin, and lower HOMA-IR (insulin resistance) as compared to those who did not use the substance.
Specifically, researchers reported that cannabis users possessed an average BMI of 26.8 compared to an index of 28.6 for non-users, after controlling for age, gender and other factors. Those subjects who reported using cannabis but never having used tobacco, or who were former users of tobacco, possessed on average the lowest BMI.
Authors concluded: “In this large cross-sectional adult survey with high prevalence of both substance use and obesity, cannabis use in the past year was associated with lower BMI, lower percentage fat mass, lower fasting insulin, and HOMA-IR. … The inverse association observed in our work supports evidence from a larger proportion of previous cross-sectional and follow-up investigations. … As a result, cannabinoids from cannabis may be viewed as an interesting avenue for research on obesity and associated conditions.”
Observational trial data published in 2013 in the American Journal of Medicine reported that subjects who consumed cannabis possessed favorable indices related to diabetic control compared to those without a history of recent marijuana use. Separate observational trial data published in 2012 in the British Medical Journal reported that marijuana users had a lower prevalence of type 2 diabetes and possessed a lower risk of contracting the disease than did those with no history of cannabis consumption, even after researchers adjusted for social variables such as subjects’ ethnicity, family history, and levels of physical activity.
Cross-sectional data published in 2011 in the American Journal of Epidemiology similarly reported that the prevalence of obesity in the general population is sharply lower among marijuana consumers than it is among nonusers.
We read with interest the recent review of medical use of cannabinoids (1). As the authors attempt to emphasize, they focus on a heterogeneous collection of experiments that employed a range of treatments, including synthetic THC, CBD, and THC-mimicking drugs.
Lay readers might inappropriately generalize these results specifically to whole plant medical cannabis But few (only two) of these experiments were conducted using medical cannabis; most of the studies reviewed focused on outcome measures that do not address the plant’s potential advantages over a single, compound agent in pill form.
For example, the authors conclude that evidence of individual, synthetic cannabinoids to help nausea and vomiting due to chemotherapy was low in quality. Within hours of the publication of the paper, mainstream media coverage applied these conclusions to medical cannabis per se, not just medical cannabinoids (2). In fact, as the authors emphasize, only 6 of the 28 studies assessing nausea and vomiting used THC, and none of these actually employed vaporized or inhaled botanical cannabis. The dependent measures were also not sensitive to the key advantage of medical cannabis for nausea: speed of onset. (Inhaled medicines can work within seconds. Sprayed extracts require at least a half hour while cannabinoids in pill form can take multiple hours.) The authors were generally careful about these caveats, but the disparate and inaccurate media coverage suggests that flagship journals in all fields now have to be even more diligent when cautioning readers about the inappropriate generalization of results. Despite increasing popularity, medical cannabis remains controversial and, apparently, newsworthy. As reviews of the effects of cannabinoids proliferate, authors, editors, journal staff, and journalists might welcome a reminder that cautions about interpretation need to be spelled out in more effusive, detailed, and thorough ways.
Mitch Earleywine, Ph.D.
University at Albany
Department of Psychology
Chair, NORML Board of Directors
National Organization for the Reform of Marijuana Laws (NORML)
Amanda Reiman, Ph.D.
Drug Policy Alliance
1) Whiting PF, Wolff RF, et al. Cannabinoids for Medical Use: A Systematic Review and Meta-analysis. JAMA, 2015: 313(24):2456-2473
2) Seaman, AM. Medical marijuana: good evidence for some diseases, weak for others. Reuters. June 24, 2015. http://www.reuters.com/article/2015/06/23/us-marijuana-medical-evidence-idUSKBN0P31WT20150623