The sweet spot study—Developing e-liquid product standards for nicotine form and concentration to improve public health: Protocol for a randomized, double-blinded, crossover study

OBJECTIVES: E-cigarettes pose significant risks to youth, but smokers may benefit from switching to e-cigarettes by reducing their exposure to toxicants, which creates a challenge for the Food and Drug Administration (FDA) in regulating e-cigarettes to protect population health. This study aims to develop e-liquid product standards for nicotine form and concentration that reduce the appeal of e-cigarettes to young people while keeping e-cigarettes available as a safer alternative for smokers. DESIGN AND PARTICIPANTS: A single-visit, double-blinded, randomized crossover design will be used to examine the effects of e-liquids with varying fractions of free-base nicotine (5%, 25%, 45%, 65%, 85%) among a sample of 66 young adult EC users and 66 older adult smokers, across ecologically valid total nicotine concentrations (20 mg or 50 mg/mL). INTERVENTIONS AND OUTCOMES: A 2-puff session will be conducted to test each of the 10 e-liquids in randomly assigned sequences, followed by a 10-minute washout period and participant ratings on appeal and sensory attributes such as throat hit and harshness, as well as behavioral intentions for continued use. Generalized linear mixed models will be used to determine a free-base nicotine level that has limited or no appeal to young adult e-cigarette users while remaining acceptable to smokers. CONCLUSIONS: This study will provide the FDA with scientific evidence regarding the effect of product standards that mandate a minimum threshold for the fraction of free-base nicotine. TRIAL REGISTRATION: The study is registered on clinicaltrials.gov under the identifier NCT05864586.