The Impact of E-liquid Propylene Glycol and Vegetable Glycerin Ratio on Ratings of Subjective Effects, Reinforcement Value, and Use in Current Smokers.

Introduction:
This text is a summary of a scientific study investigating the impact of e-liquid propylene glycol (PG) and vegetable glycerin (VG) ratio on ratings of subjective effects, reinforcement value, and tobacco use patterns in current smokers without a significant history of prior ENDS use. The study found that PG/VG ratio had minimal impact on any of the tested outcomes. Participants rated all e-liquids as less satisfying than their usual brand of cigarettes, but there were no differences between PG/VG ratios on any of the product evaluation subscales. The only exception was that participants rated the highest PG concentration (70/30) as having a stronger “throat hit” compared with the other PG/VG ratios. Use of an e-liquid at home reduced self-reported CPD and CO across groups consistent with other studies, but these results were consistent across the assigned PG/VG ratios.

Key Points:

* The study investigated the impact of e-liquid PG/VG ratio on subjective effects, reinforcement value, and tobacco use patterns in current smokers without a significant history of prior ENDS use.
* PG/VG ratio had minimal impact on any of the tested outcomes.
* Participants rated all e-liquids as less satisfying than their usual brand of cigarettes, but there were no differences between PG/VG ratios on any of the product evaluation subscales.
* The only exception was that participants rated the highest PG concentration (70/30) as having a stronger “throat hit” compared with the other PG/VG ratios.
* Use of an e-liquid at home reduced self-reported CPD and CO across groups consistent with other studies, but these results were consistent across the assigned PG/VG ratios.
* The study utilized current smokers with minimal ENDS experience, and there was no requirement that participants be interested in switching to e-cigarettes or quitting smoking.
* The most popular choice during the preference assessment was abstaining from using, which may be a reflection of task parameters.
* The results from the at-home sampling period must be thought of as exploratory due to the between-subject design, small sample size per group, and short sampling week length.

Main Message:
The main message of this study is that PG/VG ratios in the range tested have minimal impact on ratings of subjective effects and reinforcement value of e-liquids and little effect on cigarette use patterns, at least under the conditions and population studied. Therefore, regulation surrounding PG/VG ratio is unlikely to be necessary for the protection of public health. Future studies may investigate the impact of PG/VG ratio in a larger population with more varied ENDS experience and with a variety of ENDS and e-liquid characteristics.

Smith TT, heckman BW, Wahlquist aE, Cummings KM, Carpenter MJ. The Impact of E-liquid Propylene Glycol and Vegetable Glycerin Ratio on Ratings of Subjective Effects, Reinforcement Value, and Use in Current Smokers. Nicotine & tobacco research : official journal of the Society for Research on Nicotine and Tobacco. 2020;22(5):791-797. doi:10.1093/ntr/ntz130