Cannabis is an Asian herb of the family Cannabaceae—the hemp family, that has tough fibre and is often separated into a tall loosely branched species (Cannabis sativa) and a low-growing densely branched species (C. indica) [4,5]. Unfortunately, the term is used interchangeably in popular culture with marijuana although strains of cannabis can be either marijuana or hemp depending on their concentration of THC (delta-9-trans tetrahydrocannabinol).

Hemp (Cannabis sativa) is legally defined in the United States (US) [6] and European Union (EU) as any part of the cannabis plant that contains less than or equal to 0.3% THC on a dry weight basis. Hemp has traditionally been farmed for industrial uses (e.g., textiles, paper, biodiesel, constructions materials), as well as for food (hemp seeds and hemp seed oil). Typically, hemp contains relatively high amounts of non-psychoactive cannabinoids. In the US, hemp is not legally recognized as a dietary supplement for either people or animals, nor as a feed supplement for animals, so products labelled as such are illegally marketed [7]. Certain varieties of the hemp plant are legally grown in EU under license. The varieties of hemp permitted to be grown are those listed in the EU’s “Common Catalogue of Varieties of Agricultural Plant Species” [8]. The term used to describe these varieties is “Industrial Hemp”.

Marijuana refers to a mixture of cut, dried, and ground flowers, leaves and stems of leafy green cannabis plant. The term “Marijuana” is typically used for the psychoactive dried resinous flower buds and leaves of the cannabis plant (C. sativa or C. indica), but can refer to any part of the cannabis plant that contains greater than 0.3% of THC [9]. Marijuana may be smoked, vaped, or ingested (e.g., baked goods) in some countries especially for its intoxicating effect [10]. In some countries, home-made hash oil (also called honey oil or butane hash oil) is also popular. This potent oil is obtained by the extraction of cannabis using an organic solvent, often butane or n-butane [11]. Marijuana is typically classified as a Schedule 1 drug in EU countries and in the US, based on the UN Treaties on Psychoactive Substances of 1961 (revised 1971) [12]. In informal discussions, “marijuana” and “cannabis” are both terms used to describe the dried leaves and flowering heads of the cannabis plant. Subdivisions of the terms are Medical Marijuana or Medical Cannabis and Recreational Marijuana or Recreational Cannabis, despite the fact that cannabis may be marijuana or hemp depending on its THC concentration (measured on a dry weight basis). In some countries, like Canada, the term Cannabis is now used to reference all types of Cannabis to remove the stigma of the term Marijuana [13].

Cannabinoids are any of the various naturally occurring, biologically active, chemical constituents of the cannabis plants that bind to cannabinoid receptors (See Section 9 “Pharmacokinetics”). Over 480 cannabinoids and other substances have been isolated [14]. The amount of each substance contained in a sample of cannabis depends on the subspecies, the age of the plant, the time of year the leaves were harvested, the way they have been dried, and other factors [15]. During the growth of the plant, they are present in the acid forms THCa and CBDa, which through “decarboxylation” by heating transform in THC and CBD [16]. While most research has been done on the medical qualities of CBD and THC, further research is starting to look at other components of the hemp plants, such as THCa, CBDa and cannabigerol (CBG) oil [17,18].

Delta-9-trans-tetrahydrocannabinol (Δ9-THC, more commonly called tetrahydrocannabinol (THC), is the principal psychoactive constituent of marijuana [19]. THC is a lipid, assumed to be involved in the plant’s self-defence against insect predation [20], ultraviolet light [21,22], and environmental stress [23]. The concentration of THC found in plants depends on environmental conditions, including amounts of light, moisture, soil type, pH, nutrients, and trace minerals [24].

THC is the psychoactive chemical that gives marijuana performance as a recreational drug. Different components of the cannabis plant yield between 5 and 20% THC, the highest concentration produced largely by plant hairs (trichomes) and the female flower [25]. Traditionally, marijuana varietals of Cannabis sativa plants have up to 10% THC [26].

Cannabidiol (CBD) is generally made from the Cannabis sativa L. plant [17,27]. The plant contains hundreds of different active compounds and of these, more than 100 are cannabinoids which, depending on the compound, have either psychoactive or non-psychoactive effects. CBD is a non-psychoactive lipid cannabinoid [19]. CBD has been used in human medicine to mitigate anxiety [28], improve appetite [29], relieve nausea [30], control seizures of certain types [31], and assist in the management of sleep disorders [32]. Assorted CBD products are available throughout Europe for human use both online and through dispensaries [33]. A similar scenario exists in the US where CBD products are also widely available and often marketed for therapeutic purposes. To legally market such products, claims of safety and efficacy must be substantiated through the federal government approval process. If such CBD products are not granted such approval, they cannot be legally marketed and, with one exception, all products in the US that have such a therapeutic claim have not been approved [7] (See also Section 5 “The Industry of Cannabis in North America” and Section 6 “Regulatory Framework in the EU and North America”).

Resin comes from the dried leaves (‘marijuana’), the more potent female flowering heads of the plant (‘sinsemilla’), or the sticky cannabis resin that can be smoked or consumed in a variety of foodstuffs. Several cannabinoids are present in the plant resin, but THC is considered the most active and main psychoactive agent. Hashish is the resin extracted from the top of the flowering plant and is higher in THC concentration than marijuana.