If you’re worried about a purely topical CBD product getting into your bloodstream, Dr. Tishler explains that’s unlikely. CBD is hydrophobic (meaning it isn’t water-soluble) and lipophilic (attracted to lipids, like oils) and tends to stay on the outer layer of skin or possibly accumulate in the sebaceous glands unless it’s paired with “enhancers” (ingredients designed to help them make it through the skin, at which point they would instead be transdermal). Making a truly “water-soluble CBD” has been a challenge for the industry, although there are a variety of patents out there.
One major issue is that it’s actually somewhat difficult to create a topical cannabinoid product (containing CBD or THC) that penetrates the skin enough to produce an effect, but not so deep that it gets into the bloodstream, Boehnke explains. If the product does get into the bloodstream—if it’s transdermal rather than truly topical—it could potentially reach the brain, possibly producing psychoactive effects if it contains THC.
If you’re ingesting something that only has CBD in it and no THC, you won’t have significant effects in the brain. This is why CBD is often referred to as being “non-psychoactive,” although that’s clearly a bit of an oversimplification because it does do something to the central nervous system.
So…is CBD cream just an expensive placebo?
Then the researchers measured the inflammation in each rat’s knee joint, the level of CBD that made it into their bloodstream, and their pain-related behaviors. They found that the rats that were given the two highest doses of CBD showed significantly lower levels of inflammation and lower pain behavior scores compared to those that got the control. The two lower doses didn’t show much of an effect.
And even though the lotion was applied topically in the rat study, it wasn’t applied locally to the knee. Instead, the researchers were really using the topical application to get it into the rats’ bloodstream, or what’s called systemic administration. But you’d likely need a different dose for it to be effective locally (if you applied it just to your aching shoulder, for instance) in a human. We have no idea what that dose should look like.
Another study published in 2016 in the European Journal of Pain also looked at arthritis in rats but did so with a topical formulation of CBD. After the rats received an injection into one knee joint to model arthritis, they received a gel that contained either 10 percent CBD (in four different total amounts) or 1 percent CBD (the control) on four consecutive days. The gel was massaged into the rats’ shaved backs for 30 seconds each time.
All of this points to how hard it is to study the specific effects of CBD on its own—which might be why it’s tempting to claim that it’s the cure for everything without a whole lot of research to actually back up all of those claims.
Plasma concentrations (±SD) of CBD in rats with and without complete Freud’s adjuvant (CFA) induction after 4 days treatment with transdermal CBD gel.
The pro-inflammatory/pro-pain spiral is further driven by similar mechanisms which induce the expression of pro-inflammatory biomarkers in the DRG of the afferent nerves and centrally in the spinal cord. Transdermal CBD application was successful in decreasing monoarthritis-associated increases of pro-inflammatory biomarkers in neuronal tissues. Here, adjuvant-induced monoarthritis led to significant increases of TNFα expression in DRG which was decreased to baseline levels by transdermal CBD application.
2.4.3 Hindpaw thermal hypersensitivity
Animals were treated with CBD gel in four different doses: 0.62, 3.1, 6.2 and 62.3 mg/day. After four consecutive days of treatment, plasma CBD concentrations in all rats were 3.8 ± 1.4 ng/mL (n = 9), 17.5 ± 4.4 ng/mL (n = 8), 33.3 ± 9.7 ng/mL (n = 8) and 1629.9 ± 379.0 ng/mL (n = 4), respectively ( Table 1 ). The three lower doses displayed excellent linear pharmacokinetic correlation (slope = 1.0, R 2 = 0.999). However, CBD plasma concentrations after application of the 62.3 mg/day dose did not follow the linear pharmacokinetic profile.
Quantification of pro-inflammatory biomarkers in the lumbar spinal cord and dorsal root ganglia (DRG). Increases in spinal cord (A) CGRP and (B) OX42 and (C) DRG TNFα after adjuvant-induced monoarthritis are reduced to baseline levels by high doses of transdermal cannabidiol. (n = 4–6 animals per group) (*p < 0.05; one-way ANOVA).
Potential for adverse side-effects on activity levels or motor abilities stemming from CBD gel application were assessed by monitoring open-field exploratory behaviour of naive animals for 45 min prior to and directly after treatment. Irrespective of the amount of CBD applied onto the back of animals, no changes were detected for total time spent in either exploratory activity or resting ( Fig. 2C and D ). Two other specific exploratory activities acquired in the open-field test but not affected by CBD were rearing events in which the animals rise on their hindlimbs to explore the environment and the total distance travelled during the 45 min test (data not shown). This indicates that CBD did not alter the animals’ activity levels or motor abilities.