Feasibility and efficiency of cannabis vaping
The combustion and inhalation of cannabis cigarettes is generally considered an inappropriate method for the therapeutic administration of cannabis. Safer and healthier alternatives for consuming cannabis have been proposed to minimize the risks associated with the inhalation of toxic pyrolytic by-products. Vaporization conducted at less than combustion temperatures is one of the best recommended alternative methods to cannabis smoking. A vaporizer heats the cannabis plant material at a moderate temperature, causing the active cannabinoids to evaporate into an aerosol that contains far fewer harmful components. To this end, table vaporizers are commercially available (e.g., Volcano™, Storz & Bickel Gmbh); however, they are not portable, compact or sturdy. Portable, robust, low-weight, pocket pen-vaporizers are now available for nicotine inhalation. Many of these portable vaporizers can be adapted for the consumption of cannabis extracts. E-cigarettes of different brands and of varied designs could also be used for this purpose. To this end, e-cigarettes equipped with various special vaporization chambers can be used to deliver a therapeutic dose of cannabinoids. Roughly three types of devices exist on the market: those able to atomize ground plant material; those made for cannabis wax vaporization; and those intended for the atomization of liquid solutions. Vaporization of ready-to-use, pre-packaged liquids, having a certified composition and concentration, appears to be the most convenient and easiest option for therapeutic use by patients.
In this context, the possibility of delivering cannabinoids with e-cigarettes has led to a new method to administer therapeutic drugs and cannabis-based medicine, which we suggest calling “therapeutic cannavaping”. The manufacture of cannabinoids-enriched e-liquids was found to be quite difficult, and achieving a homogenous and stable mixture of high-potency waxy residues of cannabis extracts (e.g., BHO) with polar and viscous PG/glycerin commercial e-liquids is an ongoing challenge. In our study, BHO concentrations up to 10% (w/w) could be obtained. However, they were not sufficiently concentrated because inhalation of approximately 100 puffs of 70 mL would have been necessary to induce the same effects than those caused by intravenous THC administration of 1.5 mg. Preparation of liquids with higher BHO content could be of significant interest for therapeutic cannabinoids delivery as an alternative to cannabis smoking, especially for practical reasons. However, higher BHO concentrations can lead to cannabinoids solubility problems in the liquid refills. Optimization research, in particular with PG, should be undertaken to determine the best liquid refill composition offering a certified cannabinoids concentrations in the liquid and, if possible, in the vapor. Pure PG and other blends of glycols (e.g., short chain PG liquid mixtures) should be tested for the manufacture of BHO concentrates as e-liquids suitable for vaporizers and e-cigarettes.
Concerning misuse of “cannavaping”, the high number of puffs required to induce minimal psychoactive effects could be considered a rebuttal to “cannavapers” who wish to experience the same effects as real cannabis cigarettes with e-cigarette. To feel the first psychoactive effects sooner, increases in BHO levels and THC concentrations in the vaped solution are required, but due to the inconvenience in its manufacture and final organoleptic properties, such goals will be made more difficult and less appealing. In our opinion and according to other scientists, recreational “cannavaping” remains possible with e-cigarettes; however, its poor efficiency makes the risk of observing a new recreational cannavaping trend unlikely5.
Moreover, the most common commercial liquid refills (containing PG and glycerin in various proportions and often some water) are not the best solvents to solubilize BHO. Pure PG is a better solvent. Moreover, it requires the addition of flavorings as in “homemade” liquid refills because the vapors of concentrated BHO in pure PG-based liquids have been reported by users to promote throat hits, defined as pleasant feelings in throat, and to exhibit unpleasant organoleptic properties. Liquid refill choice is important to guaranteeing fair BHO solubilization and THC availability in the vapor, and it requires low glycerin content. However, glycerin is responsible for the “white vapor” noticeable when vaping devices are used, and its presence is advocated by conventional vapers. In contrast, the heating of glycerin can lead to an increase in acrolein, another toxic contaminant (not reported in our experiments because of the liquid refill composition used with no or low glycerin content). Consequently, the preparation of BHO and the making of a homogenous homemade liquid refills containing high proportions of BHO, with a pleasant taste and a fair level of glycerin, appear complex and unappealing to recreational and addicted cannabis consumers.
Thus, in our opinion, therapeutic “cannavaping” might be the most interesting outcome for the cannabinoids use with e-cigarettes. This gentle method of THC delivery could be of great importance in the context of finding new administration methods for medical cannabis. Indeed, “cannavaping” avoids the inhaling of significant amounts of toxic contaminants released during the combustion of regular cannabis cigarettes, and it guarantees soft and reproducible THC delivery if the spiked liquid refill composition is controlled. In this context, “cannavaping” could alleviate some symptoms that have been previously treated with some success with medicinal cannabis using other routes and methods of administration. “Cannavaping” could also be recommended to patients who want to quit cannabis smoking or to reduce significantly the importance and frequency of their consumption and possibly attenuate withdrawal symptoms35.
However, because the manual settings of more modern e-cigarettes can be freely adjusted by the vaper, unsafe settings can be selected to increase the efficiency of BHO and THC vaporization. It is therefore important to monitor carbonyls and VOCs contaminants to keep these potentially toxic residues in negligible quantities. Moreover, the “cannavaping” of BHO diluted in liquid refills can also lead to the formation of specific toxic contaminants. If the vaping of these liquid refills at these high settings produced unpleasant flavors due to liquid burning, these off-flavors could be masked by the fragrance of cannabis terpenoids. The results compiled in this study showed that the aerosols produced by the vaporization of BHO mixtures (up to 10%, w/w) at the highest e-cigarette settings (6.4 W, 5 V) did not generate new specific contaminants. However, these high settings were correlated with the formation of formaldehyde and acetaldehyde content in not negligible but similar amounts to those already determined with commercial liquid refills and e-cigarettes. Therefore, we advocate testing for the presence of toxic contaminants when optimizing the vaporization of cannabinoids-enriched liquid refills. In particular, we recommend determining the levels of carbonyls and VOCs contaminants, although the first results obtained at high settings did not seem to show abnormalities.
The maximal levels of power and voltage delivered by the e-cigarette were chosen to maximize the contaminants generation and the recovery of cannabinoids in the vapor. However, these settings could be ignored by vapers because of organoleptic flaws.
We used cannabinoid standards and BHO, a viscous, amber-colored, waxy cannabis concentrate, as raw cannabinoids material, but other sources, such as tinctures or macerated preparations, could be used by vapers also, although irritating ethanolic vapors could deter some users. This study specifically focused on homemade cannabinoids enriched liquid refills with BHO, but illegal liquid solutions of synthetic cannabinoids are currently available on the Internet6,36.
The most dangerous aspect of BHO concerns its preparation. Several reports of gas explosions while attempting butane extraction have been posted on the Internet. Use of a fume hood is mandatory in laboratory settings. Inhalation of traces of butane appears to pose no major health risk, although death reports correlated with butane inhalation have concerned the abuse of gas fuel among drug addicts37,38. Supercritical CO2 extraction is very likely more appropriate for preparing cannabis concentrates. CO2 toxicity is lower, and the risk of explosion is far less. However, the preparation of “CO2HO” concentrate requires more sophisticated and costlier equipment.
In the calculations, bioavailability of vaped and smoked THC is supposed to be the same. However, measurement of cannabinoids compounds in the aerosol of e-cigarettes and smoke of cannabis cigarettes does not necessarily imply equivalent absorption to the bloodstream. The different vehicles of transport of cannabis compounds could result in differences in the speed and rate of absorption from the respiratory tract. This can be assessed only by measuring plasma levels.
A limitation of the setup for the temperature measurements is that the measuring site inside the wick is not similar to the temperature on the surface of the wick where the evaporation takes place. Differences between different measuring sites may be occur, with the temperature becoming lower as you move away from the center of the coil.
Only one common type of e-cigarette was assessed for THC delivery in this study. However, other portable devices and brands with more or less sophisticated designs are currently sold and marketed. They can produce similar, but also different cannabinoids, carbonyls and VOCs amounts. Higher levels of impurities could be formed, especially with vaporizers delivering high voltages or having larger energy supplies, and a high puff frequency could lead to coil overheating and contaminant generation. Similarly, only one type of clearomizer has been tested, while many other models of e-cigarettes (with cartomizers or clearomizer/atomizers, single or dual coils, with or without wicks, for example) can be found in specialized shops and on the Internet. Their use with cannabinoids could also produce different cannabinoids, carbonyls and COVs amounts. The toxicity of the vapors generated by e-cigarettes has already been demonstrated in several studies39. However, extrapolation of these results to other models of e-devices and liquid refills is questionable.
Cannavaping appears to be a gentle, efficient, user-friendly and safe alternative method for cannabis smoking for medical cannabis delivery. Its expected benefits very likely overcome the advantages of oral administration because ingestion is characterized by its erratic absorption and poor biodisponibility. Ingested compounds that undergo first pass metabolism could be less active than inhaled compounds, which would have direct access to the bloodstream without being metabolized first. Moreover, cannavaping could avoid emesis due to strong doses of therapeutic cannabinoids when smoked or inhaled through vaporization. However, potential misuse of cannavaping has been identified, based on dabbing practices and widespread accessibility to more sophisticated e-cigarette devices. BHO can be easily extracted at home, and electronic devices specifically designed for dabbing or vaping are available on the market, as well as edible solvents to produce homemade liquid refills enriched with cannabinoids. Consequently, recreational or addictive cannavaping is theoretically possible. However, the poor solubility of BHO in commercial liquid refills (especially those with high glycerin content) prevents achieving high BHO concentrations, which are very likely preferred by recreational cannavapers and dabbing consumers. Illegal cannavaping is suspected to present a low risk of becoming popular among cannabis smokers. Public health actors and stakeholders must pay attention to this potential misuse, but safety surveys and police work should be more focused on cannabis dabbing than cannavaping. Therefore, the likelihood of misuse of cannavaping seems to be very limited, whereas therapeutic applications of cannavaping have undeniable benefits over other administration routes, with the controlled dosage of cannabinoids-enriched liquid refills. Similarly, the electronic devices commercialized for therapeutic cannavaping should be carefully studied to prevent potential overheating and contaminants generation.