CBD e-liquid: why coil resistance sets the dose

The label on a bottle states a concentration in mg of CBD per ml, which our article on dosage in mg/ml teaches you to read. How much liquid becomes aerosol at each puff is another matter, and the hardware decides it.

A 2023 study in Chemical Research in Toxicology gives figures. Tran and colleagues tested a pod e-cigarette fitted with three different coils, plus a more powerful tank device. In the authors' words, the lower the resistance, the hotter the coil and the more aerosol it forms.

Two caveats apply. The measurements were made with a nicotine liquid, and no CBD e-liquid was tested. The same study also found more carbonyl compounds, which are irritating breakdown products, per milligram of aerosol at the highest resistances. No setting wins on every count.

A rough calculation makes the gap concrete. A 10 ml bottle dosed at 300 mg holds 30 mg of CBD per ml. Assume, as a working figure, a density of about 1.15 g/ml for a PG/VG mix: 1 mg of liquid then carries about 0.026 mg of CBD. Suppose CBD passes into the aerosol in the same proportion as the liquid, which has yet to be measured. One puff would then deliver about 0.19 mg at 1.2 ohm and 0.56 mg at 0.12 ohm.

Four common atomisers were tested in a 2019 study on e-cigarette efficiency, and their operating ranges reveal two families of hardware:

The study also compares two ways of inhaling. Mouth-to-lung vaping draws the vapour into the mouth first, with a standard puff of 55 ml over 3 seconds, or 18.3 ml per second. Direct-to-lung vaping sends it straight to the lungs: 500 ml over 3 seconds, or 166.7 ml per second. Sub-ohm setups, below 1 ohm, are built for this second style.

To limit the amount per puff with a CBD e-liquid, combine a coil around 1.5 ohm, low power and mouth-to-lung inhalation.

Consumption reflects the same gap. In 2020, Hiler and colleagues asked 32 experienced users to vape freely for one hour on a single device fitted with two different coils. Their liquid contained nicotine, at 3 or 8 mg/ml.

At the same concentration, the powerful setup went through about 1.7 times as much liquid. Participants vaped less when the liquid was stronger, because users adjust their puffs to what they feel. With a CBD bottle, powerful hardware therefore empties it faster, and nothing guarantees how much is actually absorbed.

An e-liquid has two bases, propylene glycol (PG) and vegetable glycerine (VG). In a crossover trial published in 2018, Spindle and colleagues had 30 people vape four ratios on a 1.5 ohm coil at 7.3 watts. Blood nicotine peaked with the 100% PG liquid, at 13.40 ng/ml, compared with 9.59 and 8.58 ng/ml for the liquids richest in glycerine.

Participants found 100% PG less pleasant and harsher on the throat, and they drew longer puffs on the glycerine-rich liquids. These figures concern nicotine; we found no equivalent trial run with CBD. What they do show is that the ratio changes comfort as well as the amount delivered, and that no standard fixes the right mix.

Coil temperature raises a separate question. In 2021, a Hungarian team heated pure CBD between 250 and 500 °C in a laboratory pyrolyser, outside any vaping device. They measured that 25 to 52% of it was transformed, mostly into Δ⁹-THC, and also into Δ⁸-THC, CBN and CBC (Czégény et al., Scientific Reports).

In 2022, a study of real e-cigarettes, one of them set to 0.2 ohm and 200 watts, found no increase in THC in the vapour. The question is still open. Low power reduces both the amount vaporised and the heat the liquid is exposed to. For flower and resin, the settings are in our guide to vaporisation temperatures.

An e-liquid consists of propylene glycol, glycerine, flavourings and the active ingredient. Vegetable oil, MCT oil and every other kind of fat are excluded.

The reason is on record. According to the CDC, the US outbreak of vaping-associated lung injury had reached 2,807 hospitalised cases or deaths, including 68 deaths as of 18 February 2020. Investigators identified the main agent as vitamin E acetate, an oily additive put into THC liquids. It was found in the lung lavage fluid of 48 out of 51 patients and in none of the 99 controls.

MCT oils, often made from coconut, carry the CBD in oils meant to be swallowed. A 2021 study vaporised them at 215 °C in an extract vaporiser: of the 11 compounds present in the oil, 9 were found in the aerosol. CBD oil did not cause the US outbreak, and it is still not made to be vaped.

The familiar limits are 20 mg/ml of nicotine, a 2 ml tank and a 10 ml refill bottle. They come from articles 1 and 3 of the order of 19 May 2016 on vaping products containing nicotine. As its title says, the order covers nicotine liquids. It does not apply to a nicotine-free CBD e-liquid, so a 30 ml bottle is lawful.

The ban on disposable devices, on the other hand, does cover CBD. Law No. 2025-175 of 24 February 2025 created article L. 3513-5-1 of the French Public Health Code, which prohibits selling or distributing vaping devices "pre-filled with a liquid" that cannot be refilled. That article relies on the general definition of vaping products, which covers vapour "containing nicotine where applicable". The rule has been in force since 26 February 2025. Article L. 3515-3 sets the penalty at a €100,000 fine, or €200,000 for a repeat offence. The text is covered in detail in our article on the ban on puffs.

The liquid itself falls under hemp law. It may contain no more than 0.30% Δ⁹-THC, as our article on the legal THC level explains, and no HHC, H4CBD or THCP, all three classified as narcotics. The Phytogrammes catalogue has no e-liquids. If you prefer to vaporise the plant, CBD flowers have their own category.

In a 2022 study in Scientific Reports, researchers kept an e-liquid with 60 mg/ml of CBD under four storage conditions for 29 days. At 4 °C in the dark, oxidation products rose only very slightly. At room temperature, and more so at 40 °C, the CBD broke down, mostly into cannabielsoin and HU-331, a CBD quinone. Storage produced no THC.

Once a bottle is open, keep it tightly closed and away from light, in the fridge or at least somewhere cool.