This is part of a larger post that will come shortly on cannabidiol.
The best studies with the strongest evidence are designed to be the closest to what you want to know. For example, if you are a healthy and active person who wants to take CBD to reduce inflammation, hopefully there is a well-designed study in humans that examined just this. Preferably, a study like this: a cross-sectional study conducted on healthy and active people who take CBD (group 1) or a matched placebo (group 2) and biomarkers known to be associated with inflammation are compared after a certain number of weeks. This would provide good insight in to the benefits and risks of CBD use in relation to inflammation. Moreover, randomizing who is in each group is better and, if possible, blinding the subjects (or even the researchers) adds even more rigor to the study and confidence in the results. Hopefully other measures related to inflammation, such as diet and exercise, are controlled so you don’t have confounding influencers that would impact inflammation outside the influence of CBD. If not, interpretation of the results can be difficult or wrong if diet and/or exercise actually reduced inflammation but you think it was the CBD. Even within this in vivo (Latin for “within the living”) study design, hopefully the duration of the study is long enough to actually change things, and all human subjects complete the study, and the data is appropriately analyzed, and the results appropriately interpreted! There is a lot more to scientific studies than most people realize! Someone quotes a scientific article and it is more often than not considered to be a good study with accurate conclusions. But that is not always the case! Studies on humans can be difficult. I don’t think most people realize this.
There are also in vitro (Latin “within the glass”) and ex vivo (Latin “outside of the living”) studies where researchers isolate a tissue or cell from a human (or animal) and examine what happens and then speculate on whether these results will impact a human on a whole-body (i.e. in vivo) level. Lastly, there are animal studies (in vivo and in vitro), mostly in rats and mice, where they attempt to mimic human conditions of, say, inflammation (or anxiety, etc.) and then examine the results of CBD and speculate how it may or may not be similar and/or effective in a human.
The further you get away from testing what you really want to know, the weaker the evidence. So if a study showed that low doses of synthetic THC use in rats that were “depressed” from a Forced Swim Test (time of swimming to giving up in an enclosed water filled cylinder) activates a serotonin receptor (related to mental health), would you take THC (or a related cannabinoid like CBD) to help with depression? . Not to belittle this study as it is interesting and shows promising results. But the next big step to say that CBD is an anti-depressant in humans requires more smaller steps (i.e. studies). Thus, you often see in conclusions that most studies end with: more research is needed.
There are many, many studies out there. A great way to understand the current consensus on a topic is to find review or meta-analysis papers. A meta-analysis is cool because other researchers within that specific field sift through studies to find the best ones that meet their inclusion criteria. For example, a meta-analysis by Whiting et al.  was conducted in 2015 searching databases for topics related to cannabinoids and clinical trials, adverse events, and depression. Out of 23,754 title and abstract screenings, they ended up with only 79 studies that met their inclusion criteria (randomized, clinical trials in humans) . Of these 79 studies, only 1 examined anxiety disorder and zero for depression ; meaning that for these two important topics related to CBD use, there is little to no studies worth drawing conclusions from based on their inclusion criteria.
All this said, you have to be diligent in understanding the type of study and the implications of interpreting the results of such studies. Is this the utmost, best evidence? Is this good evidence? Is this weak evidence? That is why people like me, with a scientific background and research background, sift through the studies, papers, reviews & meta-analyses to inform you the reader. This of course takes trust. Am I qualified? I think so. Am I doing the best job possible? I aim to. For goodness sake, I am spending the time to explain this here [embedded within a larger post to come] where many writers don’t, which I think is important when making a decision on whether you should take CBD (or any supplement for that matter) or not. Plus, check my references, which I always include and so should all posts!
Pet-peeve: Some online articles cite in text and provide references (yay!), others don’t (boo!), and others make a citation in the text but don’t actually provide the reference at the end (what the hell?!).
I hope you learned something. I hope you understand how complicated this can be. But understanding at least what is explained above is very important to understanding recommendations for taking CBD, for taking supplements in general, and, in my opinion, understanding the relationship between research and … the universe.
More to come.
Contact me if you want to know more or have any questions!
1. Bambico FR, Katz N, Debonnel G, Gobbi G. Cannabinoids Elicit Antidepressant-Like Behavior and Activate Serotonergic Neurons through the Medial Prefrontal Cortex. J Neurosci. 2007;27(43):11700-11711. doi:10.1523/JNEUROSCI.1636-07.2007.
2. Whiting PF, Wolff RF, Deshpande S, et al. Cannabinoids for medical use: A systematic review and meta-analysis. JAMA - J Am Med Assoc. 2015;313(24):2456-2473. doi:10.1001/jama.2015.6358.