Heated tobacco: Independent scientific data calls into question the promises of harm reduction

Presented as a potentially less harmful alternative to combustible cigarettes, heated tobacco products are playing an increasingly prominent role in tobacco manufacturers' communications, who regularly put forward "harm reduction" arguments based almost exclusively on data from their own studies. Independent work published in recent years, particularly the in-depth analysis conducted by the Tobacco Control Research Group at the University of Bath,[1] and a meta-analysis published in 2025 in Tobacco Control[2], offer a significantly more nuanced lighting.

The current state of research on heated tobacco shows, first and foremost, that the available data relies largely on short-term, industry-funded trials conducted under highly controlled conditions, both methodologically and in the reporting of results, which severely limits their scientific scope. The conclusions put forward by manufacturers are not confirmed by independent studies of equivalent quality, and the current data remain insufficient to establish a measurable reduction in health risk.

Studies examining the effects of heated tobacco products primarily rely on the analysis of biomarkers of potential harm. The meta-analysis published in 2025 synthesizes research conducted between 2010 and 2024 comparing the use of heated tobacco products to the consumption of combustible cigarettes, the use of electronic cigarettes, or abstinence.

Research conducted at the University of Bath complements this approach with a critical analysis of approximately fifty clinical trials. This review focuses particularly on the quality of the protocols, the duration of follow-up, the sources of funding, and the suitability of the experimental conditions to reflect real-world use. The researchers emphasize that, unlike in the pharmaceutical sector, it is not ethically justifiable to conduct clinical trials that deliberately expose non-smokers to tobacco products in order to assess their harmfulness. This structural constraint severely limits the possibility of obtaining robust data on the relative safety of these products and prevents any direct comparison with the methodological standards applied to pharmaceuticals.

The results of the meta-analysis confirm limited and heterogeneous effects.

The meta-analysis published in 2025 in Tobacco Control This study provides a systematic overview of the evolution of a set of biomarkers used to assess the potential effects of heated tobacco products. Researchers compiled the results of studies conducted between 2010 and 2024, including measurements related to exposure to toxic substances, inflammation, cardiovascular function, and certain mechanisms associated with the development of cancers or respiratory diseases. The analysis reveals a highly fragmented picture, characterized by modest, non-reproducible, and often contradictory effects depending on the studies and parameters evaluated.

This review includes both independent work and a large number of studies funded by the tobacco industry, a choice that reflects not a methodological preference but a structural imbalance in the scientific field, where the majority of available data comes from manufacturers. The authors emphasize this limitation and recommend a cautious interpretation of the results.

Of all the biomarkers examined, only a third showed significant improvement in exclusive users of heated tobacco products compared to smokers of combustible cigarettes. These improvements mainly concerned indicators of immediate exposure to certain chemical compounds, but had little impact on biomarkers directly linked to the risk of serious illness. The authors emphasize that these effects, although sometimes statistically measurable, remain limited in magnitude and do not allow for the inference of a concrete clinical benefit.

For nearly half of the biomarkers analyzed, no significant difference was observed between heated tobacco users and combustible cigarette smokers. This lack of effect is important because it shows that switching to this type of product does not significantly alter a large proportion of health-related indicators. It also suggests that the effects highlighted by some industry studies are based on a partial selection of favorable results, without reflecting the overall state of the literature.

The meta-analysis also highlights a worrying finding: several biomarkers are evolving in an unfavorable direction for users of heated tobacco products. These negative effects notably concern inflammatory markers and certain cardiovascular indicators, two central dimensions in the pathophysiology of smoking-related diseases. These observations contradict the idea that heated tobacco is a significantly less harmful option and show that some risk mechanisms persist, or even intensify, despite the absence of combustion.

The authors of the meta-analysis emphasize a fundamental point: the clinical relevance of many biomarkers remains poorly established. Even when improvements are observed, there is no evidence to suggest that these will lead to a reduction in long-term morbidity or mortality. The heterogeneity of the results, the lack of consistent effects on key health indicators, and the shortage of long-term studies lead to a clear conclusion: current evidence does not support the claim that heated tobacco products effectively reduce health risks.

Analyses from the University of Bath highlight insufficient evidence regarding the tobacco companies' claims

The review conducted by the University of Bath is based on a systematic analysis of 49 clinical trials on heated tobacco products. This review shows that 34 of these studies, representing nearly 70 %s, were funded or conducted by tobacco manufacturers. This structural reliance on industry-sourced data inherently limits the possibility of establishing a solid foundation of independent studies to verify or counter the conclusions put forward by manufacturers.

The quality and duration of the trials constitute another major limitation. More than half of the analyzed studies lasted less than five days, which does not allow for the documentation of changes in biomarkers beyond very immediate fluctuations. Only two studies offered a follow-up period approaching twelve months, a duration that is still too short to assess the onset or progression of chronic smoking-related diseases. The researchers emphasize that this lack of longitudinal data prevents any robust conclusions on the medium- and long-term effects of heated tobacco products.

Bath's analyses also show that results observed in strictly controlled environments are not confirmed under real-world conditions. Blood pressure trials provide a striking example: some industry-funded studies report reductions in laboratory settings, but no significant improvement is observed in ambulatory trials, thus calling into question the clinical relevance of these results. This discrepancy reduces the ability to consider laboratory data as representative of users' experiences.

In this context, the fact that the trials include almost exclusively smokers is logically consistent with a harm reduction approach. However, several factors limit the ability to interpret the results. Exclusive use of heated tobacco products remains a minority practice, and a significant proportion of users engage in dual use, combining these devices with combustible cigarettes, which complicates any isolated assessment of the effects of these products. Furthermore, the issue of passive exposure to emissions generated by heated tobacco remains understudied, even though it raises specific concerns for non-smokers and those around users.

All of these factors lead researchers to a shared conclusion: current evidence does not demonstrate a tangible or lasting reduction in health risks associated with the exclusive use of heated tobacco products. The combination of studies largely funded by industry, short protocols, experimental conditions far removed from real-world use, and methodological constraints inherent to the field currently prevents these products from being considered a scientifically validated, lower-risk alternative.

Persistent uncertainties remain regarding the still poorly documented health effects.

Recent studies highlight that, despite some observed improvements in exposure biomarkers, the health effects of heated tobacco products remain largely under-documented. Available data do not allow for the establishment of a proven reduction in morbidity or mortality, largely due to the lack of robust longitudinal studies. Tobacco-related diseases, whether cancers, cardiovascular diseases, or chronic respiratory illnesses, develop over several years. However, almost all the studies analyzed cover very short observation periods, most often limited to a few days or weeks, which prevents the assessment of actual risk trajectories.

The researchers also emphasize that the biological mechanisms involved in smoking-related diseases, including systemic inflammation, oxidative stress, endothelial dysfunction, and impaired respiratory function, remain present in users of heated tobacco products. Several biomarkers associated with these processes show no improvement, and some even show an unfavorable trend, which does not support the idea of a significant reduction in risks. This persistence of concerning biological signals is a central element of the uncertainties surrounding these products.

In addition to these methodological limitations, field data further complicate the interpretation of health effects. Population studies show that exclusive use of heated tobacco products remains a minority practice, and that combined use with combustible cigarettes is very common, making it difficult to isolate the actual impact of these products on exposure and risk. In a context where dual use remains prevalent, it becomes difficult to attribute any potential improvement in biological indicators solely to heated tobacco.

Finally, the predominance of manufacturer-funded studies and the significant variability in protocols contribute to maintaining a high level of uncertainty regarding both immediate effects and long-term impacts. Experts emphasize the need for independent, rigorous studies conducted over extended periods to reliably document the health consequences of these products.

©Generation Without Tobacco

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[1] Heated Tobacco Products: evidence and insights from our research, University of Bath, accessed December 8, 2025

[2] Braznell S, Dance S, Hartmann-Boyce J, et al Impact of heated tobacco products on biomarkers of potential harm and adverse events: a systematic review and meta-analysis Tobacco Control Published Online First: 29 April 2025. doi: 10.1136/tc-2024-059000