In the present study, we demonstrated that sublingual administration of the CBDEX1
® sublingual spray, two puffs twice daily through an eight-week treatment period, could effectively improve the patient's lipid profile and glucose tolerance. Moreover, the mentioned regimen could also improve insulin sensitivity, evident from a meaningful enhancement in the HOMA2 values. Consistently, the study performed by Penner et al. demonstrated that insulin level ,HOMA-IR index, and waist circumference is lower in marijuana users than control ones (
6). Moreover, investigating the data released by the Third National Health and Nutrition Examination Survey (NHANES III) revealed that the incidence rate of DM was significantly lower among marijuana consumers compared to the non-consumer group (
4). Contrary to our findings, however, the pilot study performed by Jadoon et al. showed that a 1:1 and 20:1 combination of CBD and cannabivarin (CBV), a homolog of Δ
9-THC, could not effectively reduce fasting blood glucose level and lipid content of DM patients after a 13-week treatment period. As the administration of each drug alone could somehow affect several study's endpoint values, the authors concluded that the combination administered at the studied ratio might have an antagonizing effect on each other (
18). The first reason underlying this discrepancy is that compared to the concentrations of Δ
9-THC and CBD applied in previously performed clinical studies with meaningful positive outcomes, the one applied in Jadoon and colleague’s study was extremely low, making extrapolation of results to the higher concentration somehow difficult and doubtful (
19). Another important reason for this discrepancy may be the differences in Δ
9-THC and CBD’s root of administration. Owing to their highly lipophilic nature, Δ
9-THC, and CBD are routinely formulated as oil preparation and demonstrate a very poor oral bioavailability in humans (approximately equal to 6%) (
20).
Moreover, orally administered Δ
9-THC or CBD formulation is extensively metabolized in the liver following adsorption from the gastrointestinal tract due to CYP3A4 and CYP2C19 metabolizing enzymes activity (
20,
21). Consequently, the very low orally absorbed amount of Δ
9-THC or CBD will be immediately subjected to a large first-pass effect, only permitting an extremely low amount of intact Δ
9-THC or CBD to reach the bloodstream. In contrast, sublingual administration of Δ
9-THC and CBD can significantly improve the bioavailability of the drug (reaching a value of 20% (
20)), enhancing peak plasma concentration (C
max) of Δ
9-THC and CBD and the time required for reaching it (T
max) (
22). In this context, the large part of the sublingually administered Δ
9-THC and CBD combination can successfully bypass the first pass effect and other complications associated with the oral route administration, providing a much higher C
max and T
max values and consequently, a more rapid onset of action for Δ
9-THC and CBD in sublingual form.
Although the exact mechanism underlying the positive modulatory activity of cannabinoids on peripheral metabolism has not yet been fully understood, the activity of these compounds on CB receptors of peripheral organs may somehow explicate the answer. In this context, it has been shown that administration of rimonabant, a CB
1 antagonist, was together with a significant improvement in the sensitivity of normal mice to insulin, proposing that adiponectin may be the responsible molecule in the improvement of sensitivity to insulin (
23). This finding has also been established in human studies. Moreover, in another clinical trial, the administration of rimonabant was in a statistically significant enhancement in the adiponectin plasma concentration, weight loss, and a meaningful reduction in circumference value (
24). Additionally, the administration of cannabis to obese rats was with a meaningful increase in pancreas weight which is highly suggestive of its protective effect on beta cells viability and functionality (
25). Considering that the CB
1 receptor knockout mice are also persistent in diet-induced obesity, the role of the CB
1 receptor in metabolism and obesity becomes much bolded (
26). Since both Δ
9-THC and CBD can induce an antagonistic effect on cannabinoid receptors, it may be concluded that the observed protective effects of both compounds may be partly mediated through the enhancement of secretion of adiponectin.
As mentioned earlier, CBD is considered to be a CB
1 receptor inverse agonist, resulting in the reduction of CB
1 receptor constitutional functioning or attenuation of the endocannabinoid tone. Moreover, micromolar concentrations of CBD could show some inhibitory effects on fatty acid amide hydrolase enzyme activity and hence, can promote the accumulation of arachidonoyl ethanolamine (AEA), a well-known agonist for CB receptors. Moreover, the same concentrations from CBD could also effectively enhance 2-AG levels in humans, a selective CB
1 receptor agonist (
27). Hence, in theory, high enough concentrations of CBD may also induce beneficial lipid-lowering effects observed with rimonabant. In this context, administering 800 mcg/day of CBD in schizophrenic patients could effectively enhance plasma AEA concentrations and improve the patients' clinical signs (
9). Considering the much higher bioavailability of sublingually administered CBD, the 400 µg/day concentration from CBD may be the optimum tolerable, safe, and effective concentration for application in the clinic.
Consistent with our findings, numerous animal studies have shown glucose-controlling and lipid-lowering activities for CBD. For instance, in the study by Lehmann et al., the pretreatment of mice with CBD could delay the onset of diabetic signs (including hyperglycemia) following the induction of type I diabetes by pancreas inflammation (
28). Despite this, the study performed by Rajesh et al. demonstrated that administration of CBD could not significantly improve blood glucose levels in streptozotocin (STZ) induced diabetic mice, which may be due to the time of administration of CBD which was one-week following induction of diabetes and development of hyperglycemia, meaning that the large part of the functional beta cells may have become destroyed (
13). On another side, McKillop et al. demonstrated that administration of a synthetic derivate of CBD could lower T-CHOL and TG up to 17% and 19%, respectively, while enhancing HDL-C by 19% in STZ-induced diabetic mice (
29). Similarly, Zorzenon et al. demonstrated a significant improvement in lipid profile (including TG, T-CHOL, LDL-C, and HDL-C) of diabetic mice undergoing cerebral ischemia, treated with CBD and proposed it as an effective pharmacological agent in preventing metabolic dysfunction development in diabetic patients with cerebral ischemia (
30).
The 100 µg/10 µg CBD/Δ
9-THC 2puffs twice per day sublingually administered regimen of the present study was well tolerated by patients. Except for one case with vertigo and dizziness, no other serious adverse effects were reported. Consistently, in phase I clinical trial, evaluating the safety, tolerability, and pharmacokinetics of a CBD oral solution, most patients could tolerate up to 6000 mg/day of CBD, and none demonstrated severe or serious adverse effects at all (
31). Based on these observations, the combination of CBD/Δ
9-THC regimen could be a new therapeutic regimen for controlling the lipid profile and glycemic state of DM patients. Despite this, one of the main limitations of the present study was the low number of the studied population. Moreover, the lack of confirmatory laboratory tests, including measurement of the levels of adiponectin, resistin, GIP, Apo A, etc., is another limitation of the present study. Finally, for a more precise analysis of results, restriction or sub-classification of patients according to their receiving anti-diabetic regimen will be much more appreciated.