Own your ow legal marijuana business
Your guide to making money in the multi-billion dollar marijuana industry
Major Studies of Drugs and Drug Policy
Canadian Senate Special Committee on Illegal Drugs
Volume I - General Orientation

Chapter 5 - Cannabis: From Plant to Joint

D9THC Concentrations

The D9THC content of marijuana generally varies in natural growing conditions from 0.5 to 4%.[1][28] D9THC content serves first as a basis for distinguishing the drug type of plant from the fibre type: permitted concentrations vary by country - in Canada, as in France, it is 0.3% for the fibre type. For more than a decade now, techniques for selecting powerful strains and cultivation (in greenhouses and hydroponically) have made it possible to achieve D9THC concentrations of 15% or more. D9THC content is also used to distinguish between various cannabis products and thus to determine their price: the content of sinsemilla, for example, generally varies between 7% and 14% and is more expensive than "regular" cannabis.

The question of D9THC content, its variability, how it is determined and its effects has raised numerous issues. While all specialists agree that maximum active ingredient concentrations have increased over the past 20 years, opinion is divided on average concentrations in cannabis available on the market. Estimates vary as to the preponderance and consequences of D9THC concentrations.

First, it should be emphasized that studies show that concentrations are subject to extreme variability, for a number of reasons. First, failing a control system at source, the D9THC content of marijuana is estimated on the basis of police seizures. However, only a portion of the drug seized is analyzed for THC content,[2][29] and analyses are not all equally reliable, depending on how police or customs officials conducted the seizures and how the products were preserved and transported to the lab. In addition, between a seized product in clandestine lab or at a customs post and the product sold on the street, a number of changes can be made: tobacco, herbs and other products can be added to the gram of "pot" sold at a school which alter the nature of the drug and thus the quantity of active ingredient. This is even truer for hashish, as seen above in the example on processing in Morocco.

Second, since cannabis is a widespread illegal product, it is impossible to take a representative sample of the drug available on the market at a given time for analysis. Thus it is impossible to measure the difference between the D9THC content of cannabis seized at the production or delivery site and that of cannabis used by individuals. And third, the active ingredient concentration varies with the geographical area of origin, climatic conditions and production conditions. Likely circulating in the market at any given time is a significant variety of cannabis products reflecting the diverse conditions in which they were produced. It follows that two samples seized in Vancouver in the same week could have very different concentrations, as would be the case for samples seized the same week in Vancouver, Montreal and St. John's.

Experts told the Committee that cannabis in the Canadian market was 700% more powerful than the same drug in the 1970s. Some suggested that the average D9THC content of cannabis on the market is approximately 30%, compared to 3% to 4% in the 1970s.


The cannabis used today is up to 500 percent higher in THC - that is a range between five percent to 31 percent - than the cannabis most adults remember from the 1960s and 1970s. [3][30]


In its 1999 annual report, the Royal Canadian Mounted Police estimated the average content of seizures at 6%.[4][31] In Quebec, the Montreal Police Department asserted that the THC content of cannabis is now 25%. In a private meeting with Committee members, RCMP narcotics experts in British Columbia emphasized that it is impossible in the current state of affairs to determine the average content of cannabis in the country or in a given province, in particular as a result of the extreme variability of seizures and methods of analysis. The officers who conduct the seizures do not always pay attention to the manner in which they preserve the product, such that it may lose its D9THC content: heat, light and humidity affect the stability of cannabis. Lastly, the experts providing cannabis for therapeutic purposes whom we met said they kept various grades of cannabis, based in particular on D9THC concentrations, and that, in certain cases, the products offered to patients reached concentrations of 27%.

The most exhaustive studies on changes in D9THC levels in cannabis have been conducted in Australia, the Netherlands, France and the United States. They show, first, that more powerful products have appeared in the market beside the traditional forms of cannabis: "skunk" (a variety originating in the United States and the Netherlands), "super‑skunk" and "pollen" (stamens of male plants). Canada has not lagged behind, with BC Bud and Quebec Gold in particular.

More specifically, the studies on D9THC concentrations show similar trends:

··               In Australia, a study by Wayne and Wendy on 31,000 seizures conducted between 1980 and 1997 shows that average content varied little over the period and was between 0,6 % and 13 %. Among other things, it appears that the main development has been a more significant selection than previously of the parts of the plant with the highest concentrations.[5][32] The authors of this study make the following observation which applies equally to Canada:


A number of factors probably explain the persistence of the belief that the THC content of cannabis plants in Australia has increased 30 fold in the absence of any supporting data. First, defenders of the claim often point to reports of single samples with unusually high THC content tested by the police. At best, such samples indicate the maximum THC content that has been achieved (assuming that there were no errors in the test results) but they do not tell us what the THC content is in the cannabis that is typically used by consumers. Second, biases in the sampling of tested cannabis are amplified by the attention that the print and electronic media give to unusually potent samples, creating the false impression that cannabis with exceptionally high THC is the norm. Third, uncontested repetition of these assertions in the media has established them as “fats”; those who context these claims are asked to prove that they are false rather than the (usually nameless) proponents being asked to provide evidence that they are true. Fourth, an increase in average THC content seems to explain an apparent increase in the number of cannabis users who experience problems as a consequence of their use. [6][33]


··               In the Netherlands, the Drug Information Monitoring System of the Trimbos Institute has conducted various studies since 2000 on average D9THC content. The local variety, Nether‑Weed, contained an average of 8.6% THC in 2000 and 11.3% in 2001, whereas imported varieties were stable at approximately 5%. One of the reasons given for this difference was that the local variety was fresher and contained a lower ratio of cannabinol to D9THC. In addition, Nether‑Weed resembles sinsemilla, which comes from the unfertilized flowers of the female plant and is cultivated in greenhouses.

··               In France, the Roques report referred to concentrations of up to 20% in the case of certain Dutch hydroponic varieties.[7][34] In its recent report, France's Institut national de la santé et de la recherche médicale notes a toxicological study conducted by Mura on the D9THC concentrations of seizures since 1993. From 1993 to 1995, the average concentration was 5.5%, but approximately 8% since 1996, with spikes of up to 22%.[8][35] In 2000, 3% of marijuana samples analyzed contained D9THC levels of more than 15%.

··               Lastly, in the United States, data for 2000 show an average concentration of 6%, compared to 4.1% in 1997. In fact, recalling a study recently conducted in Mississippi, Dr. John Morgan noted:


(…) in the midst of this furore over the remarkable increases in marijuana potency, it is interesting that the potency of the commercial crop sold in the United States has not varied enormously over the 30 years that potency has been assessed by the analysis of THC content in criminally seized marijuana. In fact, I recently looked at the report, which also comes from Mississippi, that the mean THC content of some 40,000 seizures since 1974 is about three percent. It has gone up in the last 10 years. In fact, in the last 10 years I believe the arithmetic mean is more than four percent while in the 10 years before that it was about 3.5 percent. [9][36]


The following table summarizes some of the data on a historical basis for certain countries.


Year analysed

Domestic Marijuana (USA)

Foreign Marijuana (Netherlands)


Sinsemilla (USA)

Nether-Weed (Netherlands)


≥ 3 %            ≥ 5 %           ≥ 9 %

≥ 3 %            ≥ 5 %             ≥ 9 %

USA, 19961

63%                25%              3%

93%                 77%                49%

USA, 19971

63%                29%              6%

96%                 85%                64%

USA, 20002

Average of 6.07% (DEA)

Average of 13,65% (DEA)

Netherlands, 2000-20011

75%                48%               7%

93%                 87%                35%

Netherlands, 2001-20021

80%                55%               4%

100%               99%                78%

Australia, 19973

Between 0.6% and 13%


Western Australia

Average of 3,8%


Canada 19994

Average of 6%

Not available

(1)(1)     Source: Rigter H. and M. von Laar (2002) " Epidemiological Aspects of Cannabis Use", International Scientific Conference on Cannabis, Brussels, page 32.

(2)(2)     Drug Enforcement Administration, http://www.usdoj.gov/dea/concern/marijuana.html

(3)(3)     Source: Hall, W. and W. Swift (2000) op. cit., page 505

(4)(4)     Source: RCMP, Annual Report for 1999.



In short, it appears that the main change has been in maximum concentrations obtained as a result of sophisticated cross‑breeding and cultivation methods, whereas average concentrations have not significantly changed over the past 30 years.[10][37] What conclusion can be drawn from this? In the minds of some, if cannabis could still be called a "soft drug" in the 1970s, that is no longer the case today. Some are not reluctant to say it is a drug comparable to heroin or cocaine in its addictive power. As an example, the Canadian Police Association has issued the following opinion on the risks associated with cannabis.


Generally, marijuana and its derivative products are described [as soft drugs] to distance the drug from the recognized harm associated with other illegal drugs. This has been a successful yet dangerous approach and contributes to the misinformation, misunderstanding and increasing tolerance associated with marijuana use. Marijuana is a powerful drug with a variety of effects. (…) Marijuana use is associated with poor work and school performance and learning problems for younger users. Marijuana is internationally recognized as a gateway drug for other drug use. Risk factors for marijuana dependence are similar to those of other forms of drug abuse. [11][38]


Others associated the increase in demand for treatment for cannabis dependence with the increase in active ingredient concentrations. As the National Post reported:


The potent BC Bud, which has a THC content as high as 25% compared to the 2% typical in the 1970s, is also leading to health concerns in the United States. Admissions for marijuana drug treatment in Washington State now exceed the rate for treatment of alcoholism. Cannabis admissions in Cook County, Ill., have risen by 400% in the last year. [12][39]


Can it be said that cannabis has in fact become a "hard" drug like cocaine and heroin? Apart from the validity of the effects of cannabis itself as described by the Police Association, and as will be discussed in detail in the Chapter 7, that contention does not take into account the way in which the drug is used or the lack of knowledge of the effects of D9THC concentrations. Studies on the ways in which cannabis is used, considered in Chapter 6, show that regular users appear to prefer medium to mild cannabis, and that they adjust their use to the strength of the drug. Interviews with individuals who use cannabis for medical purposes tend moreover to confirm this perception. More significantly, for lack of any specific studies on the question, the effects of higher D9THC concentrations are simply not known. Lastly, as will be shown in the following section, the bio‑availability of D9THC, that is to say the proportion that is actually absorbed by the body following combustion, is highly variable. As emphasized in the report of the World Health Organization (WHO) on cannabis, considering all these factors, the actual quantity of THC absorbed by the cannabis user is difficult to estimate.[13][40] Ultimately, while it can be a legitimate preoccupation, the real issue of D9THC content has more to do with our ability to control it and better know its effects, rather than making all kinds of alarmist and unfounded statements about its level.



[1][28]  Huestis, M.A et al. (1992) "Characterization of the absorption phase of marijuana smoking", Clinical Pharmacology and Therapeutics, 52: 31‑41.

[2][29]  Note, for example, that, in the United States, there is no systematic method for measuring THC. As emphasized in a comparative analysis of changes in price of heroin, cocaine and marijuana, "Another problem is that the DEA does not test marijuana for THC content, so there is no marijuana counterpart to the pure grams reported for cocaine and heroin. The difficulty this causes is the STRIDE data provide no basis for adjusting price changes for marijuana’s quality." Abt Associates (2001) The Price of Illicit Drugs: 1981 through the Second Quarter of 2000. Washington, DC. Report prepared for the Office on National Drug Control Policy.

[3][30]  Testimony of Mchael J. Boyd, Chair of the Drug Abuse Committee and Deputy Chief of the Toronto Police Service, for the Canadian Association of Chiefs of Police, Senate Special Committee on Illegal Drugs, Issue No. 14, page 74.

[4][31]  Royal Canadian Mounted Police (1999), Annual Report.

[5][32]  Wayne, H. and S. Wendy (2000) "The THC content of cannabis in Australia: evidence and implications", Australian and New Zealand Journal of Public Health. 24: 503‑508.

[6][33]  Ibid., page 504.

[7][34]  Roques, B. (1999) La dangerosité des drogues. Paris: Odile Jacob.

[8][35]  INSERM (2001) Cannabis: quels effets sur le comportement et la santé? Paris: Les Éditions Inserm.

[9][36]  Dr. John Morgan, Professor at the City University of New York Medical School, testimony before the Senate Special Committee on Illegal Drugs, June 11, 2001, Issue No. 4, page 29.

[10][37]  ElSohly, M.A., et al. (2000) "Potency trends of delta9‑THC and other cannabinoids in confiscated marijuana from 1980‑1997", Journal of Forensic Sciences, 45(1): 24‑30.

[11][38]  Sergeant Dale Orban, Regina Police, at the Senate Committee hearing on May 28, 2001.

[12][39]  National Post, May 17, 2002.

[13][40]  World Health Organization (1997) Cannabis: a health perspective and research agenda. Geneva: WHO, 1997. On line at: www.who.org.

Library Highlights

Drug Information Articles

Drug Rehab