Background The aim of this study was to characterise all 2018 Food and Drug Administration (FDA) warning letters specific to e-cigarette products and to evaluate whether online retailers complied with FDA requested actions.

Methods All 2018 FDA e-cigarette warning letters issued by the Center for Tobacco Products to online retailers were reviewed and characterised. Date of issuance, name, type, and location of the retailer, and violation type were recorded. Retailer websites were rechecked a minimum of 30 days after the issuance of the warning letter to assess compliance with enforcement actions.

Results One hundred and thirteen of 124 letters met the inclusion criteria; one duplicate letter and 10 letters unrelated to e-cigarettes were excluded. One manufacturer was cited for associating their e-liquid with prescription drugs, and when analysed, the e-liquid was found to contain phosphodiesterase inhibitors. A majority of violations, 98.2% (111/113), pertained to the sales of an e-cigarette product to a minor and/or use of marketing that appeals to children. The majority of websites (63.7%, 72/113) resolved all violations. However, 19.5% (22/113) inactivated their website, and 16.8% (19/113) did not fully correct all violations.

Conclusions Sales of e-cigarette products to minors and the purposeful marketing of e-liquids in a manner that appeals to children and adolescents continues to be problematic. While the warning letters were successful in getting a majority of online retailers to correct the stated violation, many sold other products that would be considered a violation of marketing to minors. The appearance of e-liquids that contain prescription medications is also alarming. Comprehensive and continued enforcement of online e-cigarette retailers is urgently needed.