From the biological point of view, the psychoactive cannabinoids reported include Δ
9 THC, cannabinol (CBN), and cannabinodiol (CBND), while cannabidiol (CBD) and other cannabinoids are non-psychoactive
[10][11]. THC is the major psychoactive component and the toxicity of this metabolite of
Cannabis is the most studied
[11][25]. Its psychoactive component decreases in the order of inflorescence (the flower), leaves, stem, roots, and seeds, respectively
[10]. The interest in the potential medical use of cannabis and cannabinoids rose significantly in the 1990s, following the discovery of the endocannabinoid (eCB) system in mammals
[26]. The physiological effects of cannabinoids are exerted through various receptors, such as the cannabinoid receptors (CB1 and CB2), adrenergic receptors, and the recently discovered GPCRs (GPR
55, GPR
3 and GPR
5)
[10]. Historically, each part of the
Cannabis plant is indicated mostly for pain killing, inflammation, and for mental illnesses. For example, the
Cannabis root has been recommended for treating fever, inflammation, gout, arthritis, and joint pain, as well as skin burns, hard tumors, postpartum hemorrhage, difficult child labor, sexually transmitted diseases, gastrointestinal activity, and infections
[27].
Cannabis has also been used to treat asthma, epilepsy, fatigue, glaucoma, insomnia, nausea, pain, and rheumatism, as well as being used as appetite stimulant and a digestive aid
[26][11][2]. Since concentrations above 0.05% are pharmacologically interesting,
Cannabis inflorescence and leaf material may contain sufficient cannabinoids, mono- and sesquiterpenoids, and flavonoids for therapeutic applications
[11]. Cannabis terpenoids and flavonoids, mainly myrcene, limonene, pinene, β-caryophyllene, and cannflavin A, act in synergy with cannabinoids to induce pharmacological effects
[26]. It was proven that these compounds, which are synthetized in the aerial parts of the plant, enhance CBD’s anti-inflammatory effects and antagonize THC dysphoric action
[28]. Cannabidiol (CBD) and Cannabidavarin (CBDV) (neutral cannabinoids) have been reported to have the therapeutic potential for the treatment of epilepsy (focal seizures), as well as treating nausea and vomiting
[29][30]. Conversely, THC and CBN have been found to be active in lowering intraocular pressure, and can be applied in all cases of glaucoma that are resistant to other therapies
[23]. Cannflavin A and B are also notable flavonoids (prenylflavonoids) with medicinal potentials, such as their anti-inflammatory, anti-neoplastic, antioxidant, neuro-protective, anti-parasitic, and anti-viral effects
[31].
Cannabis female flowering tops can be simply administered through commercially available vaporizers (e.g., Micro Vape, G Pen Herbal Vaporizer, and Volcano), buccal sprays (e.g., Sativex), oral capsules (e.g., Cannador), decoctions, or oils
[26]. Only cannabis use through oral or inhalatory administration is allowed. Smoking reduces the bioavailability of cannabis ingredients by 40%, and its complete combustion can cause lung diseases and airway obstructions
[26]. Homemade decoctions and pharmacy oils are currently the most widespread cannabis formulations in Europe, making the standardization of preparation difficult
[26]. Cannabis pharmacological action is dose-dependent and can induce many adverse effects (AEs), principally related to THC, due to unintentional overdosing
[26]. The typical symptoms of cannabis acute intoxication that have been reported are dizziness, confusion, tachycardia, postural hypotension, dysphoria, panic depression, hallucinations, allergic reactions, vomiting, and diarrhea
[26][32][33]. Furthermore, withdrawal symptoms, such as irritability, aggression, anxiety, insomnia, decreased appetite, tremors, sweating, and headaches may appear after the abrupt cessation of the long-term administration of high doses of cannabis
[26]. According to the ICH efficacy and safety guidelines, it is recommended to start with low doses and increase quantities after a satisfactory period of clinic evaluation, depending on the pharmacological effects and the possible adverse effects
[34].
In the current COVID-19 pandemic, scientists are repurposing medicines (identifying new therapeutic use(s) of existing drugs) known for their biological potential (anti-viral or anti-inflammatory properties) to tackle the global issue and similar future viruses
[35]. They have hypothesized that CBD could be used as an anti-viral agent
[36] or anti-inflammatory
[37][38] tool, or to inhibit pulmonary fibrosis in COVID-19 patients
[39]. In addition, the known growing evidence of the anxiolytic effects of CBD have also been hypothesized to be used as a therapeutic option to treat long-lasting COVID-19-related anxiety and PTSD
[40], which is likely to be a significant issue of the pandemic.