The fastest way to introduce cannabinoids, like THC and CBD, into your bloodstream is through inhalation. There are several reasons that may encourage a patient to seek a rapid delivery. Conditions like migraines, panic attacks, and seizure disorders can develop quickly and have preliminary symptoms that give the patient an indication a measured cannabinoid dose is useful.
Smoking is the most common cannabinoid delivery method overall. Inhalation is also useful for its titratability. Perhaps the most desirable reason for choosing this cannabinoid delivery mechanism is its fast absorption and short time to reach peak cannabinoid plasma concentrations. Cmax, the maximum blood plasma concentration, can be reached in three to five minutes, whereas other delivery options tend to range from 20 minutes to 2 hours. Due to the traditional popularity of cannabinoid inhalation, new technologies that avoid pyrolysis and its potentially toxic byproducts have been developed. Vaporization allows cannabis consumers to inhale cannabinoids without the smoke. As vaporization technology evolves, new risks have been introduced. This article evaluates types of cannabinoid vaporization options, their respective risks and benefits.
Vaporizing mechanisms are simple designs with few parts: power source, heating element, mouthpiece, and reservoir containing cannabinoids. Vaping device reservoirs can contain cannabinoid-rich plant material, raw extract, or liquid. The liquid form of vaporizing has become the cannabinoid inhalation method of choice for many consumers. These liquids are often composed of solvents and thinning agents like propylene glycol (PG), vegetable glycerin (VG), and polyethylene glycol (PEG).
Dangers of Inhaling Vaporized Cannabis Solvents
Often consumers want higher THC plasma levels. This desire encourages the user to take larger inhalations and longer breath holds at higher vaporizer temperatures. If the liquids being inhaled are toxic or break down into toxic compounds at high temperatures, these inhalation behaviors can result in lung damage.
Electronic cigarette, or vaping, product use-associated lung injury (EVALI) is a term describing lung injuries caused by inhaling such vaporized liquids. This condition can lead to severe illness and death. The root cause of EVALI is understood in part, but not completely.  Frequent liquid vaporizing consumers who died and underwent autopsies were found to have lung damage that appeared to result from inhalation of toxic fumes and poisonous gasses.
The Centers for Disease Control and Prevention (CDC) responded with a blanket statement discouraging vaporization of such solvents and thinning agents.  Because the U.S cannabinoid industry is not well-regulated, the CDC suggested that consumers do not know what they are inhaling and should avoid such products. The CDC recommendation to abstain from vaping may be well-intentioned, but fails to address some of the benefits of inhaling vaporized cannabinoids.
Known Solvent Inhalation Risks from
Lung injury from inhaling the wrong chemicals at the wrong temperatures has been studied and is a known risk of cannabis vapor inhalation. Toxic compounds such as heavy metals, oils, oxidized lipids, aerosols, and surfactants can lead to disease and death when inhaled.
Heavy metals are commonly introduced from poorly manufactured heating coils in the vaporizing device. When the coils, which are made of metal alloys, are heated by the power supply, these toxins can be deposited into the lungs or enter the consumer’s blood supply.
…Oils, Lipids, and Solvents
Solvents can break down and form toxins, some of which are carcinogenic, at elevated temperatures. For instance, propylene glycol can break down into formaldehyde at high temperatures. Both PG and glycerol can convert to acrolein (carcinogen), glycidol (toxin with high reactivity), dihydroxyacetone (toxin) during excessive heating. 
…Vitamin E Acetate
Vitamin E Acetate has been identified as another culprit of vaping toxicity. This compound is found in corn, vegetable oil, medium chain triglycerides (MCT), coconut oil, and some petroleum-based products. Any type of lipid in the lungs is harmful and can cause a condition known as lipoid pneumonia. Inhaled vitamin E Acetate does not result in this condition though. Instead, vitamin E acetate can cause pulmonary chemical burns that compromise the lung’s fluid lining by coating the lung’s “surfactant layer”.  This unnatural lung coating blocks oxygen from transferring into the consumer’s blood stream. Such covering and chemical burns can kill lung cells. 
Benefits of Inhaling Vaporized Cannabis
While this article focuses on vaporization of cannabinoid-infused liquid solvents, discussion of two other cannabis vaporization methods (plant material and extract) are introduced first.
1. Vaporizing Cannabis Plant Materials
Inhaling cannabis plant material via heating below combustion temperatures is the safest way to introduce cannabinoids into the lungs. When done properly, this method can avoid toxic smoke inhalation. Despite the excellent safety profile of this delivery method, vaporization of plant materials is not popular, because such devices are expensive with low portability. The most common product option is the “Volcano” which retails for $500, weighs 7 pounds, and uses an electrical socket making it impractical for mobile consumers on a budget.
2. Vaporizing Cannabis Extract
Inhalation of cannabis extract can also avoid pyrolysis and toxicity (assuming the extraction method is free from residual solvents). These devices are also unpopular, because the cannabis extract is sticky. Multiple uses of such a device can become messy and reduce consumers’ eagerness for repeated use. The cost of these devices can also be prohibitive.
3. Vaporizing Cannabinoid-infused Liquid Solvents
Despite CDC claims, there is no evidence that cannabis’s psychoactive cannabinoid, delta-9-THC, is EVALI’s culprit.  Instead, unregulated carrier liquids for THC are the source of lung damage. Many cannabinoid solvents are FDA-approved and safe. If such carriers are used in allowable concentrations at safe heating element temperatures, risks associated with inhaling cannabinoid-infused liquids can be reduced.
Due to multiple deaths associated with inhalation of cannabinoid-infused liquids, concerns about the associated health risks were raised in 2019 and amplified in the US media. Sensationalism may have fueled an unnecessary panic, before data could be collected and analyzed.
One particular Johns Hopkins study was the center of media anti-vaping statements.  As pointed out by journalist Jim McDonald, the heavy metal concerns were overblown in the media. McDonald states “to reach the CDC recommended exposure limit for Aluminum (Al), a vaper [consumer of vaporizable products] would need to consume about 1.5 million grams of e-liquid in a day — or more than 3,000 pounds… all except one [metal] (nickel) would be impossible for a vaper to consume… Vaping exposures to nickel can probably be reduced or eliminated by avoiding coils that use nickel or nichrome wire… requires more than casual exposure to metals or chemicals to cause cancer or other diseases.“ 
Future and Improved Formulations
To address these vaping related risks, the National Cannabis Industries Association (NCIA) has created a Safe Vaping Task Force. This group exists to guide cannabis manufacturers towards safe product development. Such self-regulation has established recommendations for safe e-liquid products for inhalation.
These guidelines suggest the following:
Accredited labs must test cannabis products before market release
Only FDA approved additives must be considered
Food Chemical Codex, US Pharmacopeia, and FDA current Good Manufacturing Practices (cGMP) should be adhered to
Cannabis should be extracted using supercritical CO2 (to ensure no dangerous residual solvents)
Propylene Glycol and Vegetable Glycerin can be used as approved vapable solvents when used in FDA-approved concentrations (Polyethylene Glycol is not approved).
Further refinement of the NCIA guidelines should be forthcoming to ensure consumer education guides behavior away from use of unregulated compounds and appreciation for proper temperature settings.
Inhaling vaporized liquids infused with cannabinoids is a new technology that is partially understood. This delivery method introduces multiple opportunities for toxic chemicals to be inhaled. The cannabis industry is adapting to encourage safe manufacturing guidelines. Despite improvements since 2019, consumers have safer cannabinoid inhalation options (inhalation of vaporized plant material and lab-tested extracts).
Considering the newness of e-liquid vaporizing technology and its known health risks, wise consumers should avoid such inhalation methods.
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