Some say full spectrum CBD is the best (cannabidiol) CBD oil to use, and with reason. The term simply refers to a product that's not a CBD isolate—or pure CBD, with no other cannabinoids or chemicals found in cannabis. However, looking at certain pharmacokinetic and pharmacodynamic aspects of medicinal cannabis, it appears that in many cases, pure CBD is not as potent or effective as full spectrum CBD.
Just to clarify—this doesn't mean that a CBD isolate is useless, because in some cases it could be preferable to full spectrum CBD. More about that later, though.
Let's first look at how full spectrum CBD compares to pure CBD extracts for the alleviation of inflammation, pain, etc.
Source: SOL CBD
Scientific investigation the past decade or so has mainly focused on CBD isolates and their effects on different conditions.
However, researchers found every time that the CBD isolate, which was purified from all other cannabis constituents, caused what is called a bell-shaped dose-response curve.
Commenting on numerous studies, Israeli researchers note per explanation:
"Healing was only observed when CBD was given within a very limited dose range, whereas no beneficial effect was achieved at either lower or higher doses." 
In simple English, this means that in order for pure CBD to be therapeutically effective, you need to hit a specific dosing sweet spot, or the extract won't really work. In fact, taking too much could exacerbate your symptoms.
This characteristic (the bell-shaped dose-response) puts serious brakes on planning clinical and animal CBD studies, as can be expected. So, these scientists from the Lautenberg Center for General and Tumor Immunology at the Hebrew University of Jerusalem, Israel set out to find a solution for overcoming this particular dose response to CBD.
They tested a CBD isolate and an extract from a cannabis clone on mice with severe inflammation. The cannabis clone-extracted oil contained a fuller spectrum of the cannabinoid composition:
So, while it was not completely full spectrum cannabis, it did contain mostly CBD and small amounts of other cannabinoids. The small amount of THC also meant that there were no psychotropic side effects. This is, by the way, one of the attractive traits of CBD—it doesn't cause the “high” or other less pleasant side effects THC could cause.
The researchers tested the effects of the two extracts on mice with severe zymosan-induced inflammation, looking at parameters such as pain, swelling, and the Tumor Necrosis Factor (TNF). The latter is a protein associated with inflammation in the body.
The scientists observed different dose-response patterns in mice who were given the fuller spectrum CBD extract compared to a pure CBD extract.
"A dose-dependent response was observed on all three parameters tested namely, the extract prevented zymosan-induced paw oedema, zymosan-induced pain and zymosan induced TNFα production in mice, with an improved therapeutic effect upon increased dosages. Thus, the limitation with purified CBD could be overcome when presented together with other natural components of the plant."
This means that the clone extract better-prevented paw swelling, pain, and TNF production than pure CBD extract, and this effect improved when the dosage was increased.
This is good news, considering CBD's excellent side- and adverse-effect profile.
This year, in a meta-analysis of observational clinical studies on the treatment of epilepsy for which other medications don't work (refractory epilepsy), a similar finding was made. The authors concluded that, at least in patients with refractory epilepsy, spectrum CBD extracts were more effective than pure CBD, with fewer adverse effects.
Per explanation, the authors note: "The roots of this difference are likely due to synergistic effects of CBD with other phytocompounds (aka Entourage effect), but this remains to be confirmed in controlled clinical studies." 
"Entourage effect" is a label coined specifically to describe the phenomenon of all chemicals and compounds in cannabis working together better than their isolates.
THC and CBD are the most well-studied of all the cannabinoids and terpenes, and commercially, they are the proverbial poster boys (or girls) for cannabis.
Point is, while CBD is arguably found most abundantly in hemp, all its components work better together than on their own.
Marijuana, another type of cannabis, has been engineered over time to contain more THC, especially in its flowers. This is because weed's relaxing and psychotropic effects became popular to be used recreationally. As a therapeutic agent, though, THC still works better together with CBD and all the other elements in cannabis.
In fact, CBD has been found to modify the intoxicating or high-inducing effect of THC, and as demonstrated in the study discussed, only tiny amounts of THC seem to be necessary in any extract. 
That's an important point to remember. No use using full spectrum CBD and then it's laced with poisonous chemicals.
SOL*CBD is one company that focuses on the quality of its CBD product, from the organic seeds and plants to the Miron glassware in which the oil is packaged.
The company also maintains the integrity of its products by using the CO2 extraction method. It uses low heat that helps maintain the integrity of the beneficial cannabinoids and terpenes.
It is also a method that doesn't leave chemical toxins as byproducts.
While there doesn't seem to be any traceable clinical evidence that CBD extract has advantages over full spectrum CBD, there could still be a place for it.
For instance, if you live in a place with restrictive laws against marijuana and/or THC, this could be a route to take. That said—the THC content in full spectrum oil is low, and US federal law does allow for a minute amount of THC in hemp-derived CBD products.
Also, some people may have a sensitivity to one or more of the other chemicals found in cannabis—in which case, pure CBD oil would also be preferable.
RELATED: What is CBD (Cannabidiol)?
The only way to really find out which is the best CBD oil for you is by trial and error. Fortunately, cannabidiol is generally considered safe for use, even in high doses. Never attempt to self-medicate for a serious health condition, however, and always consult with your doctor if you want to supplement or replace your current chronic meds with CBD. 
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