From the desk of….

Why 0.3%?

Recently, Dr. Small replied to a question about the establishment of 0.3% as the numeric definition of hemp. This is the answer received:


I repeatedly am asked to explain the history of the 0.3% THC figure for distinguishing hemp and marijuana, and the following is the response I provide.

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 Cannabis sativa subsp. sativa as “Plants of limited intoxicant ability, Δ9-THC comprising less than  0.3% (dry weight) of upper, younger leaves, and usually less than half of cannabinoids of resin”;

and Cannabis sativa subsp. indica as “Plants of considerable  intoxicant ability, Δ9-THC comprising more than  0.3% (dry weight) of upper, younger leaves, and frequently more than half of cannabinoids of resin”.

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”.

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

                Small, E., and Beckstead, H.D. 1973. Common cannabinoid phenotypes in 350 stocks of Cannabis. Lloydia 35: 144-165.

                Small, E., and Beckstead, H.D. 1973. Cannabinoid phenotypes in Cannabis. Nature 245: 147-148.

                Small, E., Beckstead, H.D., and Chan, A. 1975. The evolution of cannabinoid phenotypes in Cannabis. Econ. Bot. 29: 219-232.

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

                Small, E., Jui, P., and Lefkovitch, L.P. 1976. A numerical taxonomic analysis of Cannabis with special reference to species delimitation. Syst. Bot. 1: 67-84.

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), and my studies simply revealed this pattern.

Nevertheless, the 0.3% criterion has indeed served as a criterion 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 be willing 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.

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.

Currently, the 0.3% criterion is somewhat of an impediment to the CBD industry (and therefore to the “hemp industry” which is increasingly turning to CBD), since few cultivars/strains are available that can produce high levels of CBD without exceeding the criterion. This is unfortunate, particularly where the THC levels are under 1%, and therefore the abuse potential is still limited. However, this is an issue for legislators to consider, and given the conservative nature of legislation concerning drugs considered to have abuse potential, is unlikely to be modified in the near future.

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.


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