Peering Through the Haze of Smoked vs Vaporized Cannabis—To Vape or Not to Vape?

We are living in an era of unprecedented rapid change to cannabis use legislation across jurisdictions worldwide. Increased availability of cannabis, and inherent perceived endorsement of its apparent harmlessness, will inevitably lead to some increase in uptake by novice or infrequent users.^1,2 Missives around potential safety of delivery by 1 method vs another circulate, yet like much of the anecdotal information that abounds, there is little scientific examination of concomitant consequences. In a placebo-controlled crossover trial conducted in healthy adults who infrequently use cannabis, Spindle and colleagues³ report a comparison of acute effects of smoked vs vaporized cannabis at 2 different doses. Dose-orderly subjective drug effects, cardiovascular effects, and impaired cognitive and psychomotor function were observed, with greater effects and higher blood cannabinoid concentrations achieved from vaporization. The authors warn that even relatively low-potency cannabis can adversely affect inexperienced users.

Acute cannabis or cannabinoid administration studies have typically shown impairment across the domains of memory, attention, and psychomotor function.⁴ The literature indicates that intravenous, smoked, and vaporized administration exerts more immediate but shorter-lasting effects than oral or sublingual routes. Spindle et al³ extend these observations by distinguishing further between smoked and vaporized routes. Of note, the same low dose of 10 mg of Δ9-tetrahydrocannabinol (THC) in cannabis resulted in significant differences relative to placebo on 16 of a total 33 pharmacodynamic outcome measures following vaporized cannabis administration, but only 8 after smoking. The higher dose of 25 mg of THC resulted in 21 and 15 significant outcomes for vaporized and smoked cannabis, respectively. Hence, vaporized low-dose cannabis produced a greater number of measurable impairments than smoked high-dose cannabis in this sample of infrequent users. These findings have implications for novice users, trying for the first time the multitude of products available legally in some US states, and believing vaporization to be a safer route of administration. Similarly, medicinal users and doctors advising patients need to be aware of the potential for vaporization to induce stronger effects, including adverse effects, and if choosing this route of administration, commence with lower doses.

Beyond an early phase of initiation, if use was continued to become frequent, tolerance may develop to some of the cognitive and subjective effects as observed in acute administration studies in frequent users; however, tolerance generally manifests as a blunted effect rather than an absence of observable effects.⁴ Not many studies have directly compared acute administration effects in frequent and infrequent users; it would be interesting to see whether vaporization relative to smoking also produces stronger effects in frequent cannabis users, particularly on the range of outcomes examined by Spindle and colleagues.³

The cannabis plant matter used in the study by Spindle and colleagues³ contained a very low proportion of cannabidiol (CBD) relative to THC. There is significant interest in the potential for CBD to ameliorate adverse effects of THC (among a range of clinical therapeutic applications) and a few vaporization studies have begun to investigate higher doses of CBD delivered by these means.⁵ It appears important to determine whether higher proportional concentrations of CBD in plant matter may protect against the greater adverse effects observed in the study by Spindle and colleagues,³ and indeed whether protection may be conferred for frequent and infrequent users alike. This evidence may be used toward informing public health policies, including recommendations to potentially increase CBD concentrations in retail products where cannabis is sold legally, to regulate the market as such, for the purpose of minimizing harms in the community.⁶ In addition, it is important to establish guidelines around recommended THC:CBD ratios, as well as the multitude of compounds in plant matter that may moderate the effects of THC, where plant matter is used medicinally.

Intrapulmonary administration of cannabinoids (eg, by smoking or vaporizing) is considered to be an effective mode of delivery owing to high systemic bioavailability, fast onset of action, short duration of peak effects, and limited duration of effects relative to other methods being considered for medicinal purposes (eg, oral, sublingual, and transdermal); more efficient and precise vaporization delivery systems are being further developed.⁷ Vaporization has been suggested as a safer intrapulmonary delivery system than smoking, since by heating rather than combusting plant matter it avoids the formation of pyrolytic toxic compounds, including carbon monoxide and carcinogens. There is, however, little robust evidence from clinical trials or epidemiological studies to support vaporization being a safer option. Further, the findings in the study by Spindle at el³ regarding blood THC concentrations do not concur with some previous research. For example, Newmeyer et al⁸ reported no difference in blood concentrations between smoking and vaporizing in occasional cannabis users, whereas frequent users had higher concentrations after smoking than vaporizing. These differences are likely owing to a range of dosing, titration, and other methodological variations between studies and call for further study and replication.

That the greater efficiency of delivery afforded by vaporization may result in stronger effects with collateral impairment should be disseminated in public health messages. Increased availability of cannabis of higher potency combined with increasing use in states where cannabis has been legalized for medicinal or recreational purposes⁹ raise public safety concerns around impairment of driving during acute intoxication. The greater cognitive and psychomotor effects of vaporized cannabis relative to smoked cannabis reported by Spindle et al,³ at a dose substantially lower than that of products available in cannabis dispensaries, further amplify these concerns around driving. In considering the relative benefits vs harms of vaporizing cannabis, one cannot help but draw parallels with the current debates polarizing the scientific research and policy around the pros and cons of electronic cigarette use.¹⁰ With further study of vaporized cannabinoids, greater evidence may converge to better inform health recommendations for both recreational and medicinal users and prescribers of cannabinoids for medicinal use.

Published: November 30, 2018. doi:10.1001/jamanetworkopen.2018.4838

Open Access: This is an open access article distributed under the terms of the CC-BY License. © 2018 Solowij N. JAMA Network Open.

Corresponding Author: Nadia Solowij, PhD, School of Psychology, University of Wollongong, Wollongong, New South Wales 2522, Australia (nadia@uow.edu.au).

Conflict of Interest Disclosures: None reported.