L. is the most cultivated, trafficked, and consumed illicit drug in the world [1
]. The United Nations classifies cannabis as all drugs derived from the plant Cannabis sativa
(Cannabaceae) containing the substance ∆-9-tetrahydrocannabinol (THC). THC is the intoxicant compound of the plant and is responsible for the classification of C. sativa
as an illicit drug. The plant also produces the cannabidiol (CBD), a compound that has been studied for pharmaceutical and medical purposes.
Aiming to increase the concentration of THC in the plant, several artificial hybrids such as “Royal AK47,” “Sharksbreath,” “Black Widow,” “Haze Prata,” “Kali Mist,” and “Jack the Ripper” have been developed through genetic selection and breeding of C. sativa
]. On the other hand, varieties such as “Cheungsam” were developed aiming at a THC/CBD ratio that is lower than 1.0 for the medicinal use of Cannabis
], while strains such as “Félina 34,” “Futura 77,” “Kompolti,” and “Carmagnola” were developed for cultivation aiming at the production of fibers [7
]. Since the morphological differentiation among all those varieties is very difficult, genetic strategies are necessary for their characterization with forensic purposes.
Forensic genetics arose as a result of the union between legal medicine and criminalistics and is most commonly linked to the use of human DNA in criminal investigations. However, the evolution of our society significantly enlarged its framework, and forensic genetics now covers a much wider range of purposes, providing subsidiary evidence in investigations involving cases such as biopiracy, bioterrorism, identification of fraudulent food composition, and identification of illicit drugs [8
Besides forensic investigations aiming to differentiate drug and non-drug varieties of Cannabis
, forensic genetics can be very useful for determining the geographic origin of seeds/plants, and for identification of traffic routes and illegal plantations. Molecular markers employed for genetic studies in C. sativa
have shown that it is possible to correlate the diversity of gene pools with their geographical origin [9
], suggesting that these biotechnological tools can be used for forensic purposes.
Taking into account the social impacts of Cannabis
traffic and its abuse, as well as recent advances in biotechnological methods, it should be expected that scientific studies on forensic genetics related to this species would have significantly increased in recent decades. An increased number of systematic reviews and meta-analyses about the medical and psychological effects of Cannabis
have been launched recently in the specialized literature [13
]. However, review studies focusing on the general patterns of scientific researches of this species, revealing trends and limitations are lacking. Such analysis might help scientists and students to identify overall research needs, to detect the scientific areas in evidence concerning Cannabis
studies, and to find reputable research centers for scientific interchange and collaboration.
Despite the importance of Cannabis for public health and security, no review or bibliometric study about the publications on this species is available in the specialized literature. In order to fill this gap, we intended to qualitatively scrutinize the patterns of scientific publications (research articles and review papers) related to Cannabis in the last six decades. In this study, we examined the main areas of interest of the researchers studying Cannabis around the world and the existing gaps concerning the current demands of research, with particular attention to forensic genetics.
The use of Cannabis as an illicit drug, particularly among younger people, represents potential harm to individuals and society, thus becoming a matter of public health. In addition, the occurrence of crimes related to the traffic of Cannabis is a problem of public security, demanding scientific strategies for forensic investigation. In particular, the use of molecular biology and genetics as tools for forensic analysis is an effective approach for the identification and traceability of Cannabis.
Our confidence in the conclusions of this study is limited by the assumption that the classifications related to the area of knowledge reflect the full content of the publications. In some cases, publications may present important information in secondary knowledge areas that are not reported in the online databases, since the indexing information is not recorded from the full discussion and conclusions of the paper. For example, the article published by Bataille and Bowen [21
] in the journal Chemical Geology
is indexed under “Earth and Planetary Science,” but it also contains important methodological insights into the traceability of Cannabis
Likewise, the geographical origin of a publication may underestimate or overestimate some countries in the case of contributions involving several institutions. In cases where students or researchers develop their studies in partner institutions with a partial PhD scholarship or as a short-term invited researcher, the authors’ affiliations in a paper may not reflect the real origin of the publication.
In addition, the question of whether the authors’ affiliation should be related to the institution of origin or to the institution where the study was developed remains unresolved. Nevertheless, our results indicate the general trends of the research centers, the main interest areas, and the major gaps in studies about Cannabis.
The results of the present study show a significant increase in scientific research related to genetics, mainly in the last two decades. However, this increase mainly concerns aspects linked to Cannabis
and human health, not to the genetics of Cannabis
. After screening articles for the search term “Cannabis
+ Forensic genetics,” only two studies out of the 26 retrieved by Scopus were related to humans (Figure S2
When analyzing the results for SNP markers found with the keywords “Cannabis and Genetics,” none of the 31 studies found was related to the genome of the plant.
Correlating this increase in scientific publications with methodological advances in DNA research [19
], it seems that only the advent of next-generation sequencing (NGS) in 2005 boosted genetics studies on Cannabis
, mainly in the last decade. Recently, NGS approaches have been employed for the complete sequencing of the Cannabis
] and mitochondria genomes [24
], to generate whole-genome drafts [25
], and for the development of SNP markers for different varieties of Cannabis
Since the use of Cannabis as a psychotropic agent is an issue of public health and its trafficking is a complex problem in many countries, controlled scientific research is essential for understanding the problems and finding solutions. There are a large number of published studies reporting the medicinal and pharmacological properties of Cannabis, as well as research related to addiction and its psychosocial aspects. However, there are few studies related to forensic genetics and traceability (29 and two publications since 1961, respectively), research areas with crucial importance for countries where the use of Cannabis has restrictions and measures to prevent the traffic are needed.
Data from the Brazilian National Secretary of Drugs Policy [26
] show that nine countries in South America, three in Central and North America, and 10 in Europe have legislation that discriminates against possession of all types of drugs. In the United States, the plant is considered prohibited, although medical marijuana is permitted in 20 states and in the District of Columbia, and recreational use is legalized in the District of Columbia, Washington, and California [27
]. In four other U.S. states, for-profit companies have been granted licenses to produce and sell a range of products for medicinal and non-medicinal use of Cannabis
. In Uruguay, the federal government approved legislation in the year 2013 regulating the cultivation, production, and recreational use of Cannabis
In a survey about the trends in Cannabis
use in 30 European and North American countries, ter Bogt and collaborators [29
] reported a significant reduction in the use of Cannabis
among 15-year-olds in the period from 2002 to 2010. However, stabilization or increase in Cannabis
use was found, particularly in emerging countries. Although the use of Cannabis
is higher in richer countries and in countries where it is readily available, the general trend revealed by the study was the former and heavier use of Cannabis
in developing countries and by less affluent youths than richer and more affluent ones. Thus, the most vulnerable countries and social groups are also the most affected by the social problems related to Cannabis
addiction, such as illegal cultivation and commercialization, violence, and psychological and cognitive health problems.
Most of the current studies on the forensic genetics of Cannabis are related to differentiation between psychotropic and medicinal varieties of this species. In addition to allowing varieties discrimination, molecular markers may be quite useful tools for the identification of traffic routes of illegally cultivated, distributed and commercialized Cannabis. Such efforts will enable more efficient prevention of the traffic in nations were Cannabis is prohibited.
There is enormous interest in research involving Cannabis and its substances, as well as in all kinds of interactions of Cannabis in humans. Along with the advances in the areas of genetics and molecular biology, the investigations have been growing and diversifying, but publications on forensic genetics and traceability are still limited. The problem of drugs is ongoing around the world and the discourse about Cannabis legalization will likely persist for many years.
Thus, a better definition of the geographic origin of plants in countries where it is prohibited is essential and, for this reason, the areas of forensic genetics and traceability emerge as primary goals. In this direction, biotechnological tools should be used for elucidation of traffic routes and for characterization of psychotropic and medicinal varieties, enabling a more efficient fight with the traffic in nations where this species has restrictions.
In general, there is a historical gap in studies on the forensic genetics and traceability of Cannabis. We expect that increasing interest in this issue and new biotechnological advances will lead to new studies using the genetics of Cannabis for forensic purposes.