When you're just starting out taking CBD oil it is important to understand bioavailability and how it differs depending on your CBD delivery method. There may also be a difference in bioavailability if you're using a nano-CBD that is water soluble vs. a typical CBD that is fat soluble.
To summarize, here are the most common methods of taking CBD oil and their respective bioavailabilites:
- Oral CBD: Approximately 6% 
- Sublingual CBD: 20-30%
- Vaping/Inhalation CBD: 30-40%
- Intranasal (IN) CBD: 34–46% 
- Transdermal CBD: Approximately 70%
- CBD Suppositories: 80-90%
- Topical CBD: Does Not Apply
When you swallow CBD the effects last longer, are slower to act, and a lot less gets into your bloodstream - 6% of what you swallow. There is also less bioavailability by a lot when you ingest and for this reason, CBD oil has a higher bioavailability than CBD capsules.
Ingestion is slower acting but it should still work but, it will just take a little longer. Some people recommend vaping while you ingest CBD because Vaping CBD acts a lot quicker. It doesn't last as long but it will last long enough to cover the time it takes for the drops to act.
Normally, less than 10% of the CBD reaches your bloodstream if you do edibles/capsules. For that reason, the best thing to do to ensure you get the highest level of bioavailability is to eat your CBD gummies very very slowly. Chew and hold under your tongue and repeat, repeat, repeat. It is most effective that way. Chew the gummy & hold it in your mouth to invest bioavailability.
For those of you eating, drinking or capsulizing your CBD please be aware that doing so reduces absorption. The fastest and most direct non-vape CBD absorption occurs under the tongue by the capillaries of that mucous membrane. Swallowing in a drink, food or capsule takes the CBD on a long detour through the digestive system which reduces absorption...stomach acids and other GI processes exert their actions on the CBD before it is absorbed by the cells lining the small intestine. A capsule is not as effective as a full spectrum CBD oil that is absorbed into your bloodstream.
Studies show a significant increase in bioavailability of vitamin C using liposomal encapsulation. Where liposomal encapsulation actually makes a difference is at a cellular level. The outer membrane of a liposome is made of similar material as a cell. For this reason, a liposome readily bonds with a cell and cannabinoids held within the liposome then are transferred to the cell from the liposome.
Taking CBD Sublingually means absorbing the CBD under the tongue, where you let the CBD oil drops soak into the little pocket that’s there. Goes straight to your bloodstream through the oral mucosa. No ingestion. No digestion. Taking oil takes a bit longer and last longer. Taking it sublingually helps it to act faster. Most people take sublingual oil at least 3 times a day: once in the morning, once in the afternoon, and once in the evening.
Vapes are faster to act but don't work for a long period. A lot of people recommend vaping to deal with anxiety because of its quick effects. Some people like CBD oil better because you know exactly how much you are dosing, whereas vaping CBD is not so clear.
Vaping is for immediate relief of symptoms, while sublingual/edible is for longer-term effects. I recommend vaping and using a sublingual.
You can mix an isolate into regular vape juice but it depends on the VG/PG ratio. You want a ratio higher in PG because isolate doesn't mix well with VG. You may also need to heat it slightly in a cup of warm water to dissolve the isolate. If you purchase a wax/concentrate pen you can vape isolate as it is using the concentrate pod, no need for mixing.
A research study found that:
"Chronic pain relief can be best achieved through the transdermal route, whereas ‘breakthrough’ pain can be best alleviated with intranasal (IN) delivery. Combining IN and transdermal delivery for CBD may serve to provide patient needs-driven treatment in the form of a nonaddictive nonopioid therapy...CBD was absorbed intranasally within 10 minutes with a bioavailability of 34–46%."
- (Cannabidiol bioavailability after nasal and transdermal application: effect of permeation enhancers.)
Transdermal CBD is different from topical CBD. These are products also applied to the skin, but it actually absorbs into the skin, penetrating through, and into your bloodstream. This means it can not only work as a localized effect but also throughout your whole body. It takes special emulsifiers and chemical compounds to make a CBD product transdermal, which is also why they tend to be more expensive. Anyone can make a topical. Not just anyone can make a transdermal, at least not safely.
CBD Suppositories are normally administered rectally, but can also be vaginal. The value/virtue of a rectal route is more bioavailability of the medication, so more relief with using LESS medication. In cases of nausea and vomiting rectal route allows the person to still get their medication. Also effective in getting the medication in the system by way of the route closest to the injury.
Using THC/ CBD rectally takes effect in about 10 minutes, total pain relief for up to 6 hours and severely cuts back on psychoactive effects since THC doesn't pass through the liver and therefore, it shouldn't affect other meds that you're taking.
First things first, (again) topical CBD and transdermal CBD and two completely different things. Topicals are what 99% of the products out on the market are. Salves, balms, roller balls, lotions, etc can all be found as topicals to buy. Topicals are applied to the skin but they only work on the skin. They generally work on the top 3 layers of the skin, and it's surrounding area, and that's it. They do not penetrate THROUGH the skin, nor does any of the CBD get into the bloodstream. If you take your sublingual CBD oil and apply it to your skin, that is topical, not transdermal. I can't apply a topical cream to my wrist and expect it to do anything for my migraine. This is largely why you can apply THC topically as well, and not experience any psychoactive effects, nor will it be likely to trigger a positive drug test.
You can’t fail a drug test with a topical And Myaderm transdermal also won’t make you fail cuz there’s no THC. Topical means it stays on the top 3 layers of skin only it doesn’t go into your bloodstream.
How to Increase Bioavailabilty?
Some people recommend using turmeric, pepper, or some other sort of oil, etc to increase the bioavailability of their CBD oil. Some studies have shown that using long-chain triglycerides (LCT) has significantly increased the percentage of bioavailability. So basically, if you want to swallow your CBD in capsules or other ways of oral ingestion do it with long chain fats like sesame oil. You'll get 20-30% bioavailability vs. 8%-12% in non-oil formulations (which even this is double or nearly triple what other sources cited have set for oral bioavailability rates).
1. ^ World Health Organization (WHO) (Geneva, 4-7 June 2018) CANNABIDIOL (CBD) Critical Review Report. (PDF) Expert Committee on Drug Dependence Fortieth Meeting. pp 11 Section 4B
2. ^ University of Kentucky (05 Nov 2010) Cannabidiol bioavailability after nasal and transdermal application: effect of permeation enhancers.