The overall purpose of this quasi-experimental study was to assess and compare the self-reported effectiveness of two THC-free CBD products – an isolate and a broad spectrum – across two independent regimens (30- and 60-day) for stress reduction. Participants reported the broad spectrum product’s effectiveness and ability to reduce stress as greater than the isolate across both regimens. However, participants preferred the taste of the isolate as compared to the broad spectrum product across regimens. There were no differences in reported adverse effects or quality between the products, regardless of regimens. Participants reported a more positive overall impression of the isolate product than the broad spectrum product, but only within the 30-day regimen. Overall, these data are consistent with the so-called “entourage effect,” suggesting that broad spectrum products containing multiple cannabinoids and other compounds (e.g., terpenes) may be more effective than isolate products [20].

Overall, participants perceived both CBD products to be effective and helpful for stress management. This finding is consistent with previous studies, demonstrating the benefits of CBD in managing stress, anxiety, and sleep problems [21]. Further, participants reported that the broad spectrum product provided more positive effects on stress management than the isolate product. Our results support the notion that cannabinoids may have synergistic effects on therapeutic outcomes [22, 23]. Indeed, prior research in patients treated for refractory epilepsy suggests that full or broad spectrum products may be superior to isolate CBD products for managing symptoms [23]. Preclinical studies have also provided some support for the entourage effect [24], but relatively few studies have been conducted in humans. In addition, other cannabinoids (e.g., THC, cannabinol, CBG) or terpenes may have significant main effects on stress reduction that could be additive, rather than interactive. Nonetheless, our results extend prior studies, suggesting that CBD may be effective for reducing stress and that cannabinoids have synergistic or additive effects. Controlled clinical studies are needed to confirm if these compounds have anti-stress properties alone or synergistically.

Although participants reported the broad spectrum product’s effectiveness and ability to reduce stress as greater than the isolate, they preferred the taste of the isolate product across regimens. With the exception of THC extraction, broad spectrum products contain all of the compounds naturally present in the cannabis plant, such as other cannabinoids, flavonoids, and terpenes, which can contribute to the taste/aroma of the plant [25]. Therefore, it is not surprising that participants preferred the taste of the isolate product over the broad spectrum. In addition, prior studies examining CBD for the treatment of epilepsy, for example, have reported that broad spectrum products have a better safety profile (i.e., fewer adverse effects) than isolate products [23]; however, we did not find a difference in adverse effects between products here. However, the number of reported adverse effects was generally low, which could have limited the ability to detect statistically significant differences. Further, adverse effects could not be attributed to a specific product or treatment duration. Future studies are needed to examine potential adverse effects more closely.

Our results should be interpreted in the context of limitations. First, the study sample was self-selected, with participants reporting an average baseline stress level of ∼8 out of 10. Therefore, responses are likely to be biased and not representative of all CBD product users. Also, both regimens started with the isolate then transitioned to the broad spectrum product, so order effects may have influenced results. Additionally, it cannot be excluded that a physiological adaptation to CBD exposure occurred over time, or that CBD effects developed from short- to long-term use, which could confound comparison between products. Future studies should incorporate blinding, a randomized controlled design, a longer treatment period, a washout period, a placebo comparator, and post-treatment follow-up assessments. Another limitation of the study was the lack of standardized self-reported measures of stress before and after the regimens. Additionally, reports of positive side effects (e.g., improved sleep, better concentration) were not collected, and participants were not asked to abstain from using other stress aids (e.g., medications, supplements) or other sources of cannabinoids or cannabis during the regimen. Future studies should also collect other demographic data, such as race, ethnicity, socioeconomic status, marital status, body mass index, and education. Nonetheless, participants were from various geographic locations across the USA (see Fig. 1) and consisted of a variety of age groups (18–79 years; see Table 1), which increases generalizability. Further, we completed two separate regimens, which allowed us to treat one as an independent replication study and importantly, our main results replicated across the independent regimens.