Deep Dive: Interview with Dr. Ernest Small

In November 2019, I interviewed Canadian senior scientist Dr. Ernest Small regarding his pinnacle—and paramountly influential—1971 book The Species Problem with Cannabis. It was this book that established the North American standard of 0.3% tetrahydrocannabinol (THC) to separate hemp and cannabis. The European Union has adopted an even more strict limit of 0.2% THC or lower to qualify as hemp in that region of the world.

Below is Dr. Small's response to my interview request, which I have lightly edited for mechanical flow and length (titles and images are mine). Thanks for helping LearnAndTeachOthers™!

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Dear Higher Learning LV,

I repeatedly am asked to explain the history of the 0.3% THC [tetrahydrocannabinol phytocannabinoid] figure for distinguishing hemp and marijuana. The following is my response.

The 0.3% dry weight figure originated from: Small, E., and Cronquist, A. 1976. A practical and natural taxonomy for Cannabis. Taxon 25: 405-435.

In that paper, we defined:

This information was subsequently interpreted in Canada's legislation as the basis of setting the limit for THC development in hemp cultivars as 0.3% THC based on: "The entire, fruit-bearing part of the plant shall be used as a sample…normally the top one-third of the plant …when the first seeds of 50% of the plants are resistant to compression."

Similarly, many countries throughout the world used 0.3% as a THC criterion for separating "industrial hemp" from "marijuana."

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The 0.3% figure was based on my previous analyses of THC content in thousands of plants:

and on mathematical analysis of the frequency pattern of cannabinoid distribution:

"Over the years, I have had many inquiries regarding whether the 0.3% criterion was based on potential for abuse—i.e. the possibility of using hemp to get high."

Over the years, I have had many inquiries regarding whether the 0.3% criterion was based on potential for abuse—i.e. the possibility of using hemp to get high.

No, it was not—the criterion was based on the pattern of variation in the real world: It happens that for thousands of years people have selected plants for fiber (subsp. sativa; low-intoxicant plants) and for marijuana (subsp. indica; high-intoxicant plants). My studies simply revealed this pattern.

Copyright © Higher Learning LV™

Nevertheless, the 0.3% criterion has indeed served as a [defining limit] for authorizing the growth of plants with extremely limited potential for abuse.

In fact, it is often pointed out that cannabis material of about 1% THC is, for practical purposes, necessary for people to...smoke it to get "high."

Accordingly, the 0.3% figure is quite conservative for purposes of limiting the abuse potential of hemp for production of marijuana-like material.

To recapitulate, the 0.3% THC figure originated on the basis of botanical classificatory considerations that reflect the real-world selection of two classes of plant—one used for fiber (and low in THC) and the other used for drugs (and of course high in THC).

As you appreciate, the figure reflects total THC (THCA + THC). The criterion was in effect determined by observation of the frequency distribution of THC in hundreds of samples of different kinds of plants (technically, by observation of the frequency of THC and correlation with other classificatory characteristics), not for legal-control purposes, but simply as an exercise in biological classification, such as is commonly done in my discipline (taxonomy).

The criterion was subsequently adopted to control cultivation of high-THC plants.

I have had considerable experience with those who prepare or modify drug legislation, and while the general intent is understood, scientific (i.e. factual) subtleties are often not understood. Nevertheless, hopefully the final legislation achieves the intended goal.

"So on reflection, the criterion has proven to be reasonable for the intended purpose, regardless of how well the framers of legislation understood the information I’ve provided above."

In the case of cannabis, the goal obviously of the widespread adoption of the 0.3% figure has been the assumption that it serves to limit the "abuse potential" of plants grown for "industrial" purposes. So on reflection, the criterion has proven to be reasonable for the intended purpose, regardless of how well the framers of legislation understood the information I’ve provided above.

Nothing in the above should be taken as an indication of how to interpret legislation in particular jurisdictions, since circumstances often differ and interpretations are often guided by different considerations.

Cordially,

Ernest Small, Ph.D., F.L.S., C.M.

Principal Research Scientist

Science and Technology Branch, Ottawa Research and Development Centre

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> The Species Problem with Cannabis by Dr. Ernest Small (1971): http://bit.ly/2K12aQf

> An interview with Dr. Small from Dec. 1999: http://bit.ly/1BRiLVo

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