Abstract
Introduction
POD electronic nicotine delivery systems (ENDS), often containing high concentrations of nicotine salts, have replaced MODs (ie, open/modifiable devices) as the most popular devices. The purpose of this study was to compare device/liquid characteristics, use behavior, and nicotine exposure between POD and MOD users.
Methods
Data from the initial visit of a prospective observational study of exclusive ENDS users compared MOD (n = 48) and POD (n = 37) users. Participants completed questionnaires on demographic characteristics, patterns of ENDS use, and ENDS features. A urine sample was collected to test for cotinine and an ENDS liquid sample was collected to test for nicotine and salts. Puff topography was captured during an ad libitum bout at the end of the session.
Results
MOD and POD users did not differ on demographic characteristics. MOD users reported purchasing more liquid in the past month than POD users (180.4 ± 28.0 vs. 50.9 ± 9.0 ml, p < .001). Differences in characteristics of devices used by MOD and POD users included flavor type (p = .029), nicotine concentration (liquids used by MOD users contained less nicotine than those used by POD users: 8.9 ± 2.0 vs. 41.6 ± 3.2 mg/ml, p < .001), and presence of the nicotine salt (fewer MOD liquids had salts present than POD liquids: 11.9% vs. 77.4%, p < .001). User groups did not differ on urinary cotinine levels or puff topography (ps > .05).
Conclusions
Despite different characteristics of MOD and POD ENDS, users of those products are exposed to similar amounts of nicotine, likely due to using more liquid among MOD users.
Implications
This study directly compares ENDS product characteristics, user behavior, and nicotine exposure between MOD and POD ENDS users. Although POD products contained higher nicotine concentrations compared to MOD products, users of PODs reported consuming less liquid than MOD users. Ultimately, MOD and POD users were exposed to similar levels of nicotine, suggesting users behaviorally compensate for differences in product characteristics.
Introduction
The electronic nicotine delivery system (ENDS) market has changed rapidly as products have evolved over time. Initial ENDS models were closed-system disposable devices that looked like cigarettes and had cartridges pre-filled with a nicotine solution of variable concentrations (cigalikes). In 2012 and 2013, these cigalikes were the most popular devices and led to ENDS market growth.1 Within a few years, open-system refillable ENDS such as MODs (eg, box-tanks) became more commonly used as the popularity of cigalikes decreased.2 These products allowed the user to refill the device with liquids containing low concentrations of nicotine but at the same time they provided greater control over device features, such as higher-powered batteries with temperature adjustment.3 A more recent trend in the ENDS market are closed-systems pre-filled with highly-concentrated nicotine solutions, such as PODs, which had risen in popularity in recent years.4,5
Key differences between MODs and PODs are: 1) nicotine form used in those ENDS (freebase vs. protonated/salt); 2) nicotine concentration; and 3) degree of user customization. In general, PODs differ from MODs in that they often contain protonated nicotine in the form of nicotine salts, typically in higher nicotine concentrations than freebase nicotine solutions used in MODs. The most common salts used in PODs include lactic, benzoic, and levulinic acids, though others may be included.6 JUUL, a leading brand of PODs, contains nicotine salts with benzoic acid and was originally labeled as having 5% nicotine (59 mg/ml), although concentrations as high as 75 mg/ml have been measured.7 By contrast, freebase liquids used in MODs often contain < 20 mg/ml nicotine.8 While MODs may allow for more device customization (eg, adjustable power, rebuildable/changeable atomizers), ease of use is a commonly noted reason for POD use.9
It is likely that MODs with freebase nicotine and PODs with nicotine salts facilitate different sensory experiences among users, leading to differences in patterns of ENDS use. For instance, nicotine salts may be more palatable than freebase nicotine at high concentrations.10 Specifically, the lower pH of nicotine salt solutions used in PODs makes them less harsh and bitter.11,12 Indeed, nicotine salts are associated with higher ratings of appeal and sweetness, and lower ratings of bitterness and harshness, compared to freebase liquids.13 The reduced harshness of protonated nicotine may allow for higher nicotine concentrations to be enjoyed without aversive effects compared to freebase nicotine solutions.14
Findings regarding absorption of different forms of nicotine (freebase vs. salt) have been inconsistent,15 though tobacco industry documents and independent study suggest that freebase nicotine is better absorbed by the user compared to salt form.12,16 Both protonated and freebase nicotine used in ENDS can deliver nicotine similar to that of a cigarette,17,18 though different nicotine concentrations and puffing patterns may be necessary to achieve these pharmacokinetic profiles. With all other variables held constant, nicotine formulation does not appear to influence the nicotine yield of an ENDS device.19
ENDS products with different nicotine concentrations may lead users to adapt their behavior (ie, compensate) to titrate nicotine levels to their preferred dose. For instance, ENDS users took more puffs, longer puffs, and ultimately consumed more liquid when using a low (6 mg/ml) compared to high (24 mg/ml) nicotine strength, though these behavioral changes were insufficient to match nicotine delivery in the 24 mg/ml condition.20 Complicating matters, different ENDS features may interact to influence nicotine delivery and subjective experience (eg, nicotine concentration × power).21 For instance, vapers using fixed-power devices increased their daily vaping time over 5 days, but puffing remained stable when power settings were adjustable.22 Indeed, ENDS users may compensate for lower nicotine concentrations by using higher wattages and consuming more liquid.23 Vapers also may puff less intensively on higher wattage devices, but still consume more liquid and nicotine.24 However, titration of nicotine dose has not been compared between different device types, which is further complicated by different nicotine formulations (freebase vs. salt).
It is likely that ENDS with low-concentrated freebase nicotine (MODs) and ENDS with highly-concentrated nicotine salts (PODs) facilitate different user experiences, particularly related to patterns of use and nicotine intake, though these differences have not been widely studied. The purpose of the current study was to compare users of MOD and POD ENDS. Specifically, we investigated if these users differed in their demographic characteristics, patterns of ENDS use, liquid characteristics used in ENDS, and nicotine exposure.
Methods
Study Participants
Data come from the initial visit of an ongoing cohort study that observes ENDS users over 12 months. Inclusion criteria for the cohort study included: 1) age 18–54 years old; 2) healthy based on self-reported medical history; 3) no acute respiratory illness in past 30 days; 4) use of flavored ENDS daily for the past 6 months (with or without nicotine); and 5) no cigarette or smokeless tobacco use in past 6 months (self-reported). Exclusion criteria included: 1) history of respiratory allergy; 2) health conditions and therapies that may affect immune response or inflammatory markers (eg, asthma, aspirin/NSAID therapy, COPD, etc.); 3) pregnancy or lactation; 4) concurrent participation in another clinical trial; 5) unable to communicate in English; and 6) Unable/unwilling to follow protocol. An additional inclusion criterion for the current analysis was the use of MOD or POD ENDS devices (definitions below).
Study Procedures
Data were collected from February 2019 to June 2021 in Buffalo, New York, and come from the initial visit of an ongoing cohort study of ENDS users. The initial session lasted approximately 45–60 minutes and occurred in the following order. First, participants consented to participation and were screened for eligibility. Eligible participants completed questionnaires on demographics, smoking and ENDS use history, ENDS devices and flavors, and respiratory health, among others (relevant questionnaire codebook in Supplemental Materials). Samples of exhaled breath condensate, blood, urine, saliva, oral cells, and nasal epithelium were collected for analysis of biomarkers related to exposure and harm (only urinary cotinine data reported here). Several respiratory tests (eg, spirometry, FeNO) were conducted to measure respiratory function (data not reported here). Participants were asked to bring their current ENDS products to the initial visit. Study technicians took detailed pictures of the products. At the end of the visit, participants were asked to engage in an ad libitum puffing bout for an undefined amount of time. Participants were paid $30 for participating in the initial visit. All procedures were approved by the Roswell Park Comprehensive Cancer Center Institutional Review Board (I-70618).
Participant Demographics and Nicotine Use History
Questions adapted from the Population Assessment of Tobacco and Health (PATH) survey were administered to assess demographics (eg, age, sex, race, education, income, employment), drug use, medication use, and diet. Questions adapted from the PATH survey also were administered to assess lifetime and current use of tobacco products. Specific questions assessed smoking status (100 + cigarettes lifetime) and how long former smokers have remained abstinent from cigarettes. Participants provided a detailed history of ENDS use, including history of switching from tobacco to ENDS, frequency of ENDS use, use of flavored ENDS, liquid purchasing practices, and commonly used ENDS brands. The study questionnaire is provided in Supplementary materials.
Characterization of ENDS Products
Individual ENDS characteristics self-reported by study participants included if the device was rechargeable, if the device was refillable and how liquid was stored (tank, non-refillable cartridge, refillable cartridge, other, don’t know), if voltage was adjustable (yes, no, don’t know), brand, and liquid flavor. Flavors were grouped into fruit, tobacco, menthol/mint, sweet, ice (combination flavor + cooling sensation), other, or multiple flavors. Device type (MOD vs. POD) was solely categorized by having two researchers (NF, NL) code pictures of participants’ most commonly used device in the past month (ie, participant self-report was not used to determine device type). MODs were defined as large box- or tube-shaped devices that contain a refillable tank, customizable components, and switches/dials/buttons to adjust power or temperature (eg, relatively more complex/requires assembly). PODs were defined as compact and slender devices that contain a removable pod or cartridge that may be pre-filled or refillable (eg, relatively more convenient/more standardized).
Measurement of ENDS Use Behaviors
Participants self-reported how long they had been using ENDS and how many ml of liquid they purchased in the past month. Puff topography was measured during ad libitum puffing bout with a CReSS Micro monitor with a connecter for ENDS products, which has been used previously to measure ENDS puff topography.25,26 The topography monitor was calibrated before each session using a smoking machine and a square-shaped puff profile.26 Topography variables included puff count, puff duration (s), interpuff interval (IPI; s), puff volume (ml), and puff flow rate (ml/s). Puff topography data were manually cleaned using a standardized procedure that combined two puffs that were separated with an IPI < 300 ms and deleted any remaining puffs that were < 300 ms duration.27,28
Analysis of Nicotine Solutions
One to two drops (~0.25 ml) of e-liquid was collected from MOD participants during an initial study visit. Aliquots were collected into a 1.5 ml Eppendorf tube and stored in 4°C in dark space. A used cartridge or closed device was collected from POD participants during the same visit and stored in the same location until analysis. E-liquid from used POD cartridges or closed devices was extracted using centrifugation. Liquid samples were analyzed for nicotine concentration, type of nicotine salts, and propylene glycol to vegetable glycerin ratio using gas chromatography–mass spectrometry (GC–MS) as described in Supplementary material.
Assessment of Nicotine Exposure
A urine sample was collected from participants and immediately aliquoted and stored in a −80°C freezer. Cotinine, a metabolite of nicotine, was quantified using ultra performance liquid chromatography–tandem mass spectrometry (UPLC–MS/MS) as described previously.29,30
Statistical Analysis
MOD and POD users were compared using chi-squared analyses (categorical outcomes) and independent samples t-tests (continuous outcomes). Tests were considered statistically significant at p < .05. Analyses were conducted in IBM SPSS Statistics 25.
Results
Demographics and Nicotine Use History
Among 114 ENDS users who participated in the cohort study, 85 were included in the analytical sample (n = 20 excluded for using other device types; n = 9 excluded for using multiple device types). Other devices (excluded from analysis) included cigalikes (n = 2), eGo-style pens (n = 4; ie, refillable tank without battery modifiability), and modern disposables (n = 14; eg, Hyde, Puff Bar). Of the 85 included participants, 48 used MODs and 37 used PODs.
Demographic characteristics of MOD and POD users are demonstrated in Table 1. MOD and POD users did not differ on any demographic characteristics. MOD and POD users also did not differ on most cigarette smoking history variables: 91.7% of MOD and 90.2% POD users had ever taken a puff from a cigarette; 75.0% of MOD users and 65.9% of POD users had smoked 100 + cigarettes lifetime; 89.6% of MOD users and 94.6% of POD users reported not smoking any cigarettes in the past 30 days (ps > .05; Note: the pattern of results did not change when those who reported smoking in the past 30 days were removed from analyses, and thus, they were included). Among those that had smoked 100 + cigarette lifetime, MOD users reported quitting smoking for longer (n = 35; 50.0 ± 6.2 months) compared to POD users (n = 24; 30.8 ± 6.6 months), t(57) = 2.06, p = .044. MOD users reported using their ENDS for longer (65.6 ± 4.7 months) compared to POD users (45.0 ± 5.7 months), t(83) = 2.82, p = .006.
Table 1.
Demographic Characteristic Comparisons Between MOD and POD Users)
| MOD user | POD user | X 2 or t | p | |
|---|---|---|---|---|
| Age (years) | 29.1 (1.1) | 26.8 (1.4) | 1.35 | .18 |
| Gender | 0.23 | .63 | ||
| Male | 64.6% | 59.5% | ||
| Female | 35.4% | 40.5% | ||
| Race | 6.98 | .14 | ||
| White | 91.7% | 91.9% | ||
| Black | 2.1% | 0.0% | ||
| Asian | 0.0% | 8.1% | ||
| Multiple | 4.2% | 0.0% | ||
| Other | 2.1% | 0.0% | ||
| Education | 1.57 | .67 | ||
| <High School | 2.1% | 2.7% | ||
| High School Degree | 31.3% | 21.6% | ||
| Some College | 37.5% | 35.1% | ||
| College Degree | 29.2% | 40.5% | ||
| Employment | 10.58 | .06 | ||
| Working | 79.2% | 45.9% | ||
| Temporary Off | 2.1% | 5.4% | ||
| Looking | 4.2% | 8.1% | ||
| Disabled | 2.1% | 5.4% | ||
| Student | 10.4% | 24.3% | ||
| Other | 2.1% | 10.8% | ||
| Income (in thousands) | 9.93 | .27 | ||
| <25 | 6.3% | 21.6% | ||
| 25.01–50 | 27.1% | 29.7% | ||
| 50.01–100 | 35.4% | 18.9% | ||
| 100.01+ | 25.0% | 21.6% | ||
| Refused | 6.3% | 8.1% |
Values represent Mean (±SE) or percent of participants
Product Characteristics Reported by ENDS Users
All POD ENDS and 97.9% of MOD ENDS were self-reported as rechargeable. All MOD users self-reported that their device stores liquid in a tank. POD users were more mixed in their responses: 43.2% tank, 27.0% non-refillable cartridge, 16.2% refillable cartridge, 5.4% other, 8.1% don’t know; Χ2(4) = 36.18, p < .001. A larger percentage of MOD devices had variable/adjustable voltage (87.5%) than POD devices (16.2%), Χ2(2) = 46.13, p < .001. The most popular brands of MODs were GeekVape (22.9%), VooPoo (20.8%), and SMOK (18.8%), with 37.5% using other brands. The most popular brands of PODs were SMOK (48.7%) and JUUL (29.7%), with 21.6% using other brands. MOD and POD users reported currently using different flavors, Χ2(6) = 14.05, p = .029. Though fruit was most common in both MOD and POD users, a higher percentage of MOD users reported fruit flavors (64.6%) compared to POD users (36.1%). By contrast, more POD users reported using menthol/mint (25.0% vs. 4.2%) and tobacco (16.7% vs. 6.3%) flavors compared to MOD users.
Patterns of ENDS Use
MOD users reported purchasing significantly larger quantities of liquids in the past month (180.4 ± 28.0 ml) compared to POD users (50.9 ± 9.0 ml), t(83) = 3.94, p < .001 (Figure 1, Panel B). Topography data were missing for 20 MOD and 17 POD users due to CReSS device failures (n = 4), inability to connect ENDS to CReSS (n = 31), or participant forgetting ENDS (n = 2). MOD and POD users did not significantly differ on any puff topography measurement (ps > .05). On average, MOD users took 6.3 ± 0.7 puffs during the ad libitum session, with an average puff duration of 1.8 ± 0.2 sec, an average puff volume of 139.3 ± 14.1 ml, an average flow rate of 73.8 ± 4.03 ml/s, and IPI of 12.5 ± 1.0 s. POD users took an average of 7.5 ± 0.8 puffs during the ad libitum session, with an average puff duration of 1.7 ± 0.2 s, an average puff volume of 126.2 ± 13.4 ml, an average flow rate of 74.9 ± 3.5 ml/s, and IPI of 11.7 ± 2.8 sec.
Figure 1.
Comparison of average nicotine concentration measured in liquids extracted from MOD and POD ENDS devices (mg/ml; Panel A); average volume of liquid purchased in past month by MOD and POD ENDS users (ml; Panel B), and average cotinine concentration measured in urine samples collected from MOD and POD ENDS users (ng/ml; Panel C). Error bars represent standard error of the mean.
Results of Laboratory Analysis of ENDS Products
Thirteen participants were missing data for liquid analyses due to not bringing their product or an insufficient volume for analysis. Nicotine concentration (mg/ml) was significantly lower in MOD liquids (8.9 ± 2.0) than POD liquids (41.6 ± 3.2), t(71) = 9.20, p < .001 (Figure 1, Panel A). MOD liquids had significantly lower PG to higher VG volumetric ratio (PG = 36.3 ± 1.6; VG = 63.7 ± 1.6) compared to POD liquids (PG = 44.0 ± 1.8; VG = 56.0 ± 1.8), t(71) = 3.19, p = .002. More POD liquids contained nicotine salts (77.4%) compared to MOD liquids (11.9%), Χ2(1) = 31.97 p < .001. The most common salts identified in POD liquids included benzoic acid (58.3%), lactic acid (37.5%), and levulinic acid (4.2%). Of the n = 5 MOD liquids with nicotine salts, 80% included lactic acid and 20% included benzoic acid.
Nicotine Exposure
Cotinine levels did not significantly differ between MOD (1487.2 ± 146.6 ng/ml; median = 1285.9 ng/ml) and POD users (1187.6 ± 143.2 ng/ml; median = 866.8 ng/ml), t(80) = 1.43, p > .05 (Figure 1, Panel C). Supplementary Figure 1 shows the distribution (histograms) of urinary cotinine concentrations among MOD and POD users.
Discussion
This study is one of the first direct comparisons of MOD and POD ENDS users regarding demographic characteristics, nicotine use history, product and liquid characteristics, patterns of ENDS use behavior, and nicotine intake. The study revealed that MOD and POD users do not differ on their demographics, but they do differ substantially in their product and liquid characteristics. As expected, ENDS products used by POD users contained much higher nicotine concentrations than products used by MOD users. Nicotine salts were more frequently detected in POD compared to MOD ENDS. Although MOD users used liquids with lower nicotine concentrations, they reported using larger quantities of liquid compared to POD users. Ultimately, MOD and POD users did not differ in their cotinine levels, suggesting comparable nicotine intake from both ENDS types.
The novel finding reported in this study is that despite the large difference in nicotine concentration between MOD and POD ENDS products, users of those ENDS types had comparable urinary cotinine concentrations, suggesting similar exposure to nicotine. The discrepancy between nicotine concentration in a product and marker of exposure (cotinine concentration in urine) may be a result of MOD users purchasing, and likely consuming, more liquid in the past month, which is evidence of behavioral compensation and consistent with reports that MOD users use higher wattages and consume more liquid.23 Similar salivary cotinine levels have been reported between JUUL users, users of other ENDS, and dual cigarette-ENDS users, and were slightly lower than cotinine exposure in cigarette smokers.31 Similar results were found in this study, with comparable urinary cotinine levels in different ENDS users but lower than levels in cigarette smokers.32,33 In contrast, adolescent POD users have demonstrated higher cotinine levels than non-POD users, though not all participants used ENDS daily.29 Urinary cotinine levels observed in the current study are higher than those reported among adolescent dependent POD users,29,34 though this finding is unsurprising due to the current sample being adult and mostly former smokers. The implications of this level of nicotine exposure should be assessed regarding nicotine dependence and withdrawal intensity in ENDS users. It will also be important to compare the health effects of these products, as it is possible that MOD users will be exposed to more harmful constituents through inhaling larger quantities of aerosol generated at higher temperatures.8
Our findings on product and liquid characteristics are consistent with previous research. High nicotine concentrations in nicotine salt liquids have been observed previously in POD ENDS.6 By contrast, MOD users predominantly report using low nicotine contents (eg, <20 mg/ml).35 Additionally, lactic, benzoic, and levulinic acids have been identified as the most common acids in nicotine salt liquids,6 which was replicated in the current study. The use of higher VG/lower PG ratios in both MODs and PODs are consistent with research suggesting that PG-dominant liquids may be less pleasant and satisfying to ENDS users,36 though the VG:PG ratio was more even in POD liquids compared to MOD liquids. High prevalence of tobacco and menthol flavors in PODs may be related to the FDA policy to remove unauthorized flavored cartridges from the ENDS market in January, 2020 (note: approximately 50% of sample was collected pre-announcement and 50% post-announcement).37 Later in May 2020, the New York State ban on all flavored nicotine products took effect.38 It is likely that this statewide flavor ban will have a larger impact on MOD users, who commonly use fruit and sweet flavors as also observed in national datasets.35,39 However, fruit flavors were still most popular among POD users, which may be indicative of pre-flavor ban data collection or suggest that retailers and consumers are circumventing this flavor ban. Surprisingly, puff topography did not differ between MOD and POD users despite differences in device and liquid characteristics. However, the puff durations observed in this study (~2s) are substantially shorter than what has been measured among experienced ENDS users (~3–4.5 s).17,25,27,36 The shorter puff durations observed in the current study may be a function of study design. Participants were not asked to engage in pre-session abstinence, and this non-deprived state may have reduced their desire to puff or puff intensity compared to a deprived state.40,41 Additionally, the ad lib bout was not a standardized duration (ie, participants could stop whenever they wanted), which allowed participants to stop puffing sooner to leave the session. Finally, the CReSS monitor is validated to measure cigarette puff topography,42 but not ENDS puff topography. One study has determined that CReSS can be used for ENDS puff topography measurement, but only provides accurate measurement under certain parameters (eg, lower flow rates).43 Puff topography should be compared between MOD and POD users using a study design optimized for this measure and using a validated ENDS topography device such as the eTop.27
This study has several limitations that highlight opportunities to extend this research. Notably, the lines between device types are becoming less clear. For instance, the SMOK Nord 2 is a device that uses refillable PODS but also allows for changing atomizers and adjustable voltage, thus making it unclear if this device is a POD, MOD, or combination of the two. The terminology used between researchers and users is not always consistent,44 which may explain the mixed responses regarding how liquid is stored in PODs. Additionally, a sample of 85 participants from the same geographic region limits the generalizability of these results to the greater population. Our sample was largely former-smoking young adults, and may not apply to nonsmoking adolescents, older adults, or dual users. Similar analyses should be replicated in population-level datasets such as Population Assessment of Tobacco and Health Study (PATH) to assess the representativeness of these findings. Self-reported product characteristics (eg, adjustable voltage, liquid storage) were not verified for accuracy by the research team. Additionally, we relied on self-report of ENDS use behaviors. Future studies may consider studying ENDS use in the natural environment with ecological momentary assessment methods to better characterize ENDS use behavior. Similarly, quantity of ENDS consumption was based on purchasing behavior, rather than self-reported consumption. Detection of the nicotine salt lactic acid is tentative, given several limitations by the instrument in chromatographically resolving this chemical. Mainly, fragmentation leads to low molecular weight ions which fail to meet the minimum threshold (30 amu) measured by the instrument detector. Only the primary fragmentation ion (45 amu) was used to identify this salt in e-liquids where other nicotine salts were not present. Finally, this study was limited in scope to behavior and product characteristics. Future studies should determine if MOD and POD users differ in liquid toxicant constituents, biomarkers of harm and exposure and experience different acute or chronic health problems.
This study demonstrates that despite differences in product and liquid characteristics, MOD and POD ENDS users are exposed to similar levels of nicotine exposure. These findings have important policy implications since they suggest that regulating specific device types or nicotine concentrations may not be sufficient methods to limit nicotine exposure in ENDS users. The study suggests that potential behavioral compensation (eg, more consumption of ENDS product to titrate nicotine exposure) may occur especially among experienced and long-term ENDS users in response to changes in ENDS product characteristics. Future studies can test this hypothesis more directly by having users switch devices/features to determine the user response to potential regulations. Importantly, little is known about the health consequences of freebase vs. salt nicotine in human subjects, and the potential harms associated with different nicotine forms or device types may be future targets for regulation.
Supplementary Material
A Contributorship Form detailing each author’s specific involvement with this content, as well as any supplementary data, are available online at https://academic.oup.com/ntr.
Contributor Information
Nicholas J Felicione, Department of Health Behavior, Roswell Park Comprehensive Cancer Center, Buffalo, NY, USA.
Lisa Kaiser, Department of Health Behavior, Roswell Park Comprehensive Cancer Center, Buffalo, NY, USA.
Noel J Leigh, Department of Health Behavior, Roswell Park Comprehensive Cancer Center, Buffalo, NY, USA.
Michelle K Page, Department of Health Behavior, Roswell Park Comprehensive Cancer Center, Buffalo, NY, USA.
Ashleigh C Block, Department of Health Behavior, Roswell Park Comprehensive Cancer Center, Buffalo, NY, USA.
Bradley E Schurr, Department of Health Behavior, Roswell Park Comprehensive Cancer Center, Buffalo, NY, USA.
Richard J O’Connor, Department of Health Behavior, Roswell Park Comprehensive Cancer Center, Buffalo, NY, USA.
Maciej L Goniewicz, Department of Health Behavior, Roswell Park Comprehensive Cancer Center, Buffalo, NY, USA.
Funding
This work was supported by the National Cancer Institute at the National Institutes of Health and the Food and Drug Administration Center for Tobacco Products (grant number U54 CA228110)
Declaration of interest
NJF, LK, NL, MP, RJO: None to declare. MLG has received a research grant from Pfizer and served as a member of scientific advisory board to Johnson & Johnson.
Data availability
Data will be available upon reasonable request.
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Data Availability Statement
Data will be available upon reasonable request.