3. Potential Uses for Hemp in North America
While there are as many as 50,000 uses claimed for hemp products , there are only a few hemp products with the potential to generate a significant market. Three major product categories with market potential are: (1) fiber; (2) oilseed; and (3) pharmaceuticals.
Hemp fiber constitutes an outer ring of long phloem fibers (“bast” or “bark”) and an inner core of short xylem (“wood”) fibers, the former of much greater value than the latter . The inner core of short, stiff, xylem fibers along with remnants of the stem pith are collectively called hemp hurds. The outer primary phloem fibers of the stem grow very long in amalgamated bundles, and are supplemented by secondary phloem tissue produced to the inside of the primary phloem and composed of much shorter fibers. Long bast fibers are valuable, short bast fibers are less valuable, and hurd fibers are about half the value of bast . Separation of bast from hurds is called “retting”, with several methods for selectively removing pectic substances that bind the bast fibers to the less desirable parts of the stem. Bast fibers are preferred for automotive applications, and making specialty papers and textiles. Hurd fibers are primarily used for animal bedding and hemp–lime construction applications, and sometimes also for fiberboard .
The world hemp fiber market has been relatively stable the past 20 years  (Figure 2), even though EU hemp production was reinitiated during this period and fiber production peaked in the late 1990’-s  (Figure 3). The FAO data provided in Figure 3 appears to differ substantially from recent European Industrial Hemp Association  data for 2013, particularly for hempseed production. European hemp production initially focused on fiber, and the industry has been heavily subsidized by the EU. While synthetic fibers are derived from fossil fuels, natural fibers are extracted directly from plant and animal species, with cotton (Gossypium spp.) and wool as the primary examples, and flax (Linum usitatissiumum L.), sisal (Agave sisalina Perrine), jute (Corchorus sp.), kenaf (Hibiscus cannabinus L.), and abaca (Musa textilis L.) as examples of natural fibers with niche markets. Cotton accounts for about 85% of the natural fiber textile market worldwide, while hemp accounts for less than 0.5% . Although hemp pulp is not as profitable as wood pulp, and hemp has more environmental concerns regarding water consumption, soil erosion, and soil nutrient depletion , a niche market in Europe has developed for hemp cigarette paper. High quality bast is used along with other natural fibers for a variety of fiber biocomposites for automobiles [14,15]. Hemp has about a 15% market share of the EU automobile biocomposite industry, while about 15% of the total hemp fiber produced in the EU is used for automobile biocomposites .
Figure 2. World hemp fiber production, 1961–2013. Source: .
Figure 3. European Union fiber and hempseed production, 1993–2013. Source: .
From a building materials standpoint, hemp and other natural fibers have light weight, high strength to weight ratio, high insulating potential, and are more recyclable than conventional materials . Hemp–lime construction can include hemp–lime concrete (hempcrete), natural fiber insulation, or hemp–lime stucco, with environmental and economic benefits . Hemp–lime concrete is a mixture of a lime-based binder and relatively inexpensive hemp hurds, and is considered carbon negative . Hemp–lime construction is used throughout Europe, but use of hurds for this purpose competes with the lucrative animal bedding market, which uses about half the hurds produced in the EU . Hurds can be an economically viable alternative bedding for both large and small animals . Hemp fiber also has potential as a biomass source, as described later in Section 7.5.
Breeding for fiber has a long history, with relatively modest gains anticipated in the near future. Hemp has limited potential to garner a significant market share as a natural fiber crop. Although there are many applications that can substitute hemp fiber for conventional products, the non-hemp versions are always more economical. Hemp pulp is about five times as expensive as wood pulp in Europe . Cotton likely will remain a more attractive option for apparel. China has well established spinning facilities for natural fibers and coupled with a cheap labor force this makes establishment of a hemp textile industry outside of China problematic. There is a very dedicated niche market for environmentalists interested in hemp building materials, hemp clothes etc., but such uses are not likely to increase greatly. USA imports of hemp yarn have increased over the past couple of years  (Figure 4), but in general USA hemp fiber imports are relatively stagnant compared to hempseed imports (Figure 5). Even with significant subsidies, European hemp fiber production has not greatly expanded, and it is highly unlikely that either Canada or the USA would consider any form of hemp subsidy.
Figure 4. Value (USD) of USA imports of hemp fiber products, 2006–2015. Source: .
Figure 5. Value (USD) of USA imports of hempseed and hemp oil products, 2006–2015. Source: .
Hempseed has been used as food for at least 3000 years for both humans and livestock , and hempseed was one of the “five grains” of ancient China . Hemp oil was also used as a lighting oil, and for making soap, paints and varnishes in the past. Twentieth century usage of the grain was confined mostly to bird seed, and oilseed land races of hemp were abandoned. Relatively recently, oilseed cultivars were bred in both Europe and Canada . There is limited evidence that significant domestication occurred in the past specifically for harvest of seeds for human consumption, although a few land races in China have large seeds used as snack food. By comparison, most domestication for low-THC hemp was for fiber characteristics. In the last two decades, there has been increased selection specifically for seeds, and the few cultivars that have been developed represent only a limited amount of the potential for oilseed qualities and productivity. Hulled hemp seed, canned or vacuum-packed, recently has become a popular food for human consumption. The gritless seed meal produced by hulling differs from the oil-poor seed cake remaining after oil has been expressed, which also has been referred to as seed meal .
Vegetable oils extracted from seeds can be used as food, biofuel, nutritional supplements, and a wide variety of industrial applications. However, at present hempseed and hempseed oil is economically significant mostly as a minor specialty crop furnishing a niche food market. About 90% of the edible oil production worldwide comes from palm (Arecaceae spp,), soybean (Glycine max (L.) Merr.), canola (Brassica napus) and sunflower (Helianthus annuus L.) . Hempseed oil can be pressure-extracted on either a small or large scale, using screw or hydraulic presses, which extract 60%–80% of the oil . The residual pumace can be pressed into an ‘oil cake’ (seed cake) which in reality is a de-oiled cake. The protein-rich seed cake remaining after oil has been expressed has been shown to be an excellent livestock feed . Hempseed oil also can be extracted with n-hexane solvents , although this typically results in a contaminated final product unsuitable for human food or animal feed . It is possible to use supercritical CO2 extraction to produce food quality hempseed oil , but it is costly and time consuming.
Hempseed oil is a vegetable or fixed oil from the seed (achene), and is best used as a fresh uncooked (salad) oil. The smoke point of hempseed oil is approximately 165 °C, which is too low for high temperature cooking or frying . Approximately 80% of the fatty acids in hempseed oil are unsaturated , giving it a relatively short shelf life, which can be extended by storing in dark containers and by refrigeration.
Hempseed oil is rich in both omega-6 and omega-3 essential fatty acids, with a ratio of omega-6 to omega-3 considered optimal for human health [22,29]. Hempseed oil contains significant quantities of γ-linolenic acid (GLA), and smaller concentrations of other fatty acids of dietary significance . Aging, diet and pathology may impair GLA metabolism, and supplementation in the diet can have a positive effect on many disorders . Antioxidant tocopherols of the Vitamin E group are present in hempseed at higher concentrations than flax and canola seed oils , with about 80% of tocopherol present as γ-tocopherol [24,33]. Sterols up to about 0.7% of the oil are present in hempseed oil , and have a desirable antioxidant function. Phenolic compounds also are effective antioxidants providing cardio-protection and anti-inflammation benefits. Hempseed is rich in phenolics, with almost a four-fold range in concentration among current cultivars .
As with any grain crop, the primary breeding goal is increased yield, which must include selection to reduce seed shattering. Most breeding for oilseed characteristics has taken place in the past decade and it is likely that significant advances in oilseed composition can be made in the near future . Oilseed characteristics of accessions and cultivars have been evaluated in Canada , China , Germany , Pakistan , and Romania . One essential goal of any breeding program is to keep THC levels as low as possible. The United Kingdom prohibited marketing of the very popular oilseed cultivar, FINOLA, in January 2016 for exceeding the authorized THC content two years in a row , however the European Commission decision to authorize the prohibition was recently repealed . It appears that a number of compositional traits are significantly influenced by environment, particularly latitude. Mölleken and Theimer  determined that hempseed grown in northern regions has a much higher concentration of GLA, compared to hempseed from more southern regions.
Currently, oilseed hemp is not competitive with linseed (Linum usitatissimum) for manufacturing oil, neither is it competitive with sunflower or canola for edible vegetable oil . Nevertheless, economic prospects for a hemp oilseed crop in North America are promising, as the demand for hempseed products (seed, oil, and oil cake) is steadily increasing  (Figure 5). USA hempseed imports increased from $29 million in 2014 to $54 million in 2015, and hemp oil cake imports doubled over that period to $16 million. Total USA imports of seed, oil, and oil cake products exceeded $75 million in 2015. Hempseed production in the European Union (EU) has increased greatly  (Figure 3), and was as high as 73,450 tonnes in 2012. However, unlike Canada where hempseed is mainly employed as human food, in Europe the seed has been predominantly employed as livestock feed.
Cannabis contains a relatively unique class of terpenophenolic compounds—the cannabinoids. There are well over 100 different cannabinoids  produced in epidermal trichomes, but few are present in appreciable quantities, and relatively few have adequate pharmacological data available. Trichomes are epidermal appendages present on aerial parts in most plant species with many proposed functions, usually considered protection against predators [44,45]. There are several classes of epidermal secretory glandular trichomes in Cannabis, all of which produce cannabinoids . Most THC is located in the resin heads of capitate-stalked glandular trichomes . The highest concentration of cannabinoid resin is found in trichomes on the perigonal bracts which envelop the pistils and seeds. Glandular trichomes are also concentrated on the lower surface of young leaves, and on sepals and anthers. The primary cannabinoids produced in glandular trichomes are shown in Figure 6. The non-intoxicant cannabigerol (CBG) is the precursor of the other cannabinoids. Cannabichromene (CBC) is a non-intoxicant type found in trace amounts. There is generally an inverse relationship between THC and CBD in Cannabis; marijuana types produce primarily THC, while industrial hemp types produce primarily CBD . Moreover, marijuana biotypes produce considerably more cannabinoids than do industrial hemp cultivars. Cannabidiol (CBD) antagonizes the intoxicant effects of THC . Cannabinol (CBN) is a degradation product (Figure 6), not found in appreciable quantity in fresh plants. The THC in stored marijuana gradually converts over time to CBN, which is estimated to have 10% of the psychoactive potential of THC . Cannabidiol can be converted to THC by acid catalyzed cyclization, but this is not a practical method for generating THC.
Figure 6. Biosynthetic pathways of the principal cannabinoids. CBG = cannabigerol; CBC = cannabichromene; CBD = cannabidiol; THC = Δ9-tetrahydrocannabinol; CBN = cannabinol.
Marijuana is chemically characterized by high amounts of THC while hemp is characterized by high amounts of CBD, but the psychopharmacological distinction between THC and CBD is somewhat problematical. As discussed by Small , the pharmacological classification of marijuana is controversial, and numerous terms have been applied to it and to THC in particular. These include psychedelic (mind-manifesting or consciousness-expanding), hallucinogenic (hallucination-producing), psychotomimetic (psychosis-imitating), illusinogenic (illusion-producing), psychodysleptic (mind-disrupting), psychoactive (altering sensation, mood, consciousness or other psychological or behavioral functions), psychotropic (mind-altering), and psychotomimetic (mood-altering). Several of these terms apply to CBD, not just to THC. A psychoactive drug acts primarily upon the central nervous system where it alters brain function, resulting in temporary changes in perception, mood, consciousness and emotion. A psychoactive drug is a psychotropic substance. Since CBD has anti-anxiety, anti-psychotic, and anti-depressant effects, it is correctly considered a psychoactive drug .
Cannabidiol was first isolated from Cannabis in the late 1930s , and has since been found to have therapeutic potential for disorders such as inflammation and anxiety, and also has potential as a neuroprotective agent and an antioxidant [52,53]. Along with CBD, other minor cannabinoids such as cannabidiolic acid (CBDA), tetrahydrocannabinolic acid (THCA), and cannabidivarin (CBDV) have shown efficacy for relief of nausea and emesis . Cannabidiol also has been used to treat arthritis, cancer, diabetes, neurodegenerative diseases and pain . Indeed, CBD has many more medical applications than THC , and since CBD is the principal cannabinoid of hemp it is arbitrary to refer only to high-THC biotypes of C. sativa as “medical cannabis”. Oilseed cultivars produce more flowers than fiber cultivars, and since the principle source of resin is from flowering tops, oilseed cultivars are a much more promising source of CBD than fiber cultivars . At present, however, selected biotypes are being employed to produce CBD commercially—strains that not only produce mostly CBD by comparison with the yield of THC, but also produce much more CBD than conventional industrial hemp cultivars.