The Issue of Cannabis

A brief review of current knowledge about marijuana, the most controversial among all illegal drugs

Marijuana plantThe issue of cannabis legalization has proved to be the most controversial among all illegal drugs, a controversy often grounded on ideology rather than evidence, on either side of the debate. The question of the dangers of cannabis is at the heart of the debate over drug liberalization, so anyone who wants to get an objective opinion on the matter should be able to rely on scientific knowledge. Unfortunately, it is clear that discrepancies abound across studies, while supporters or opponents of liberalization do not hesitate to draw premature conclusions from these studies.

Cannabis is probably the substance which has advanced the most in the way of a regulated liberalization, for several reasons: it is a substance perceived as less dangerous than others; it can be cultivated easily; and finally because several states or countries have already taken the plunge and abandoned repression-based policies to implement decriminalization (Portugal) or regulated legalization (states of Colorado and Washington, Uruguay, the Netherlands). Moreover, from the beginning of the 2000s, several countries, including Canada, have begun to make a distinction between cannabis medical use and recreational use.

According to the World Drug Report by UNOD, it is estimated that between 125 million and 227 million people have used cannabis in 2012, i.e. between 2.7 and 4.9 % of the world population aged 15-64 (6). The market for cannabis (herb and resin) continues to grow; it is the primary substance of abuse in two thirds of the countries and between 2006 and 2010 there has been a significant increase in cannabis-related hospitalizations (59 %), and treatment admissions have increased by 14 %.

Cannabis and Repression

Until recently cannabis use was prohibited in all countries. Since 1961, cannabis and its derivatives are listed in Schedule 1 of the 1961 convention, as a drug presenting ” a significant risk of abuse”, like opium or cocaine. Accordingly, the use and possession of cannabis have been criminalized in most countries.

Today, more and more voices challenge these laws that seem to cause much more harm than good. In the United States and other countries, the simple fact of smoking a joint of cannabis can result in a jail sentence. Furthermore, even though drug users do not necessarily do jail time, the consequences for the lives of people can be devastating: revocation of a professional license, inability to obtain insurance or mortgage or to access public jobs, loss of voting rights, etc

THC Concentration

It is often said, by the police, officials and even cannabis users, that currently available cannabis plants contain up to thirty times the active ingredient, THC (tetrahydrocannabinol) than in the 70s,  in the era of Flower Power, which would explain the increased harm caused by cannabis, especially among young people.

In fact, according to the few studies (1) that are available on the subject, the dosage of THC has increased, but much less than usually thought (studies show that THC average concentration has increased from 1.2 % to 4.2% and in some cases to 6.3%). Actually, what has really changed is the preference choice of users, especially among young people, for the flowering tops (the “heads” of the plant). In these flowering tops have THC concentration is much higher than in the leaves. Similarly, the widespread use of water pipes, or bongs, in some countries, again particularly among young people, increases the capture of active substance in each inhalation (2).

Consequences of Cannabis Use

Physical Health

The evaluation of the effects produced by cannabis on health is problematic for several reasons: it is an illegal substance whose consumption can be hidden; the drug is often mixed with tobacco smoke; cannabis is sometimes associated with lifestyles that can influence the onset of various diseases; and finally, for economic reasons the drug is often adulterated with potentially more harmful substances. These difficulties can be a source of discrepancies between studies, depending on the degree of integration of these factors.

Epidemiological research does not provide a definitive answer about the dangers of exposure to long-term cannabis smoke, particularly in relation to cancer risk. However the following has been shown:

  1. As for any combustion of organic matter, cannabis smoke contains carcinogens, however, the carcinogenic effect of tobacco smoke cannot be applied as such to cannabis ;
  2. An important use can cause respiratory pathologies;
  3. The risk of developing respiratory diseases appears to be increased by the particular way cannabis is used: unfiltered, deep inhalations and prolonged retention of smoke into the lungs.

Intellectual and Emotional Development of Young People

The physical pathologies related to cannabis are rare complications; however the daily consequences of cannabis use are particularly harmful to younger consumers. Towards the beginning of adolescence (between 12 and 14 years old), cannabis use is often associated with poor school performance, high absenteeism, early school leaving, and it seems that there is a correlation between cannabis use and alteration of emotional development.

In addition, research indicates that repeated cannabis use is associated with a decline in cognitive processes and a significant decrease in IQ. However, there is no definite evidence about the irreversible nature of this or cognitive impairment.

Mental Health

Research has shown that people with mental health problems (anxiety, depression or psychosis) are more likely to be cannabis users or had used before for long periods of time. Regular use of cannabis doubles the risk of developing a psychotic episode or develops schizophrenia. Research suggests a strong link between early cannabis use and mental health problems (schizophrenia or bipolar disorder) further in genetically vulnerable people, especially teenagers.

Violence and Aggression

People who consume cannabis at an early age are at greater risk of developing problems of violence and / or crime, however, research has not determined whether this is due to the fact that people with these tendencies (violence and other psychosocial problems) are also more likely to use cannabis. In addition, illegal context in which individuals seek cannabis appears to increase the risk of violence.

Physical and Psychological Dependency

For a long time it was estimated that cannabis was not an addictive substance because users had no such symptoms associated with abstinence from alcohol or opiates. Contrary to these beliefs, experimental research has shown that an important use of cannabis can cause a syndrome of physical and psychological withdrawal similar to tobacco, but of lesser magnitude than that of other drugs, such as alcohol or heroin.

Therapeutic Uses

Marijuana State-issued card

The use of cannabis for medical purposes has a long history in Asia, India and the Middle East. The first mention of medicinal use of cannabis comes from ancient China, nearly 5000 years ago. Gradually, the therapeutic properties of cannabis were rediscovered by the West: in the nineteenth century, several articles were published in Europe and cannabis appeared in the official American pharmacopoeia in 1851 as a sedative, analgesic and antispasmodic. It remained on sale until the advent of prohibitionist laws of the 30s.

Since the 1990s, cannabis and its derivatives have attracted growing interest among laboratories. Between 2000 and 2007, over 9,000 scientific papers have been published, a figure that has more than doubled in ten years. These studies suggest certain properties of medicinal cannabis, especially to relieve the side effects of chemotherapy for patients with AIDS, but also for its antispasmodic, anti -emetic, and appetite stimulation (9).

It is however recommended to take several forms non-smoked cannabis, to avoid toxicity associated with the combustion of the substance: drug (dronabinol – Marinol®), inhalation by vaporization, herbal tea, or buccal spray and other forms.


This brief review of the literature shows that cannabis is far from being a harmless substance as is often described by its supporters. We must remember clearly: Cannabis is a drug whose harmfulness is increasingly documented. Recent research shows in particular the risk of using this substance for mental health, especially among young people.

On the other hand, policies and campaigns, which have pointed to demonize cannabis for decades, have not only been ineffective but also, they have paradoxically contributed to strengthening the distrust of users and potential users to the “prevention messages” associated with a drug wrongly perceived as relatively harmless. Therefore, it is essential to reconcile these audiences with prevention messages that concern them. This can only be done by providing information on cannabis that is clear, objective and compared.

(1) See in particular: Potency Monitoring Project (University of Mississipi, USA) – a study on 51,037 samples collected between the 70’s and 2003

(2) National Household Survey, 1998, mentioned by Jan Copeland & al. Australian National Council on Drugs, 2006

(3) Evidence-based answers to cannabis questions, a review of the literature – Australian National Council on Drugs, 2006