Do Nicotine Lozenges Actually Cause Cancer?

Nicotine lozenges have not been shown to cause cancer in humans, and nicotine itself is not classified as a carcinogen by any major health authority. The largest and longest human study to date, which followed participants for years after randomization to nicotine replacement therapy, found that NRT use was not a significant predictor of lung cancer, gastrointestinal cancer, or cancer of any kind. That said, the story is more complicated than a simple “no,” because nicotine does interact with cells in ways that concern researchers, and the kind of decades-long data that would truly settle the question does not yet exist.

What the Human Evidence Actually Shows

The most direct evidence comes from the Lung Health Study, a large clinical trial that randomly assigned some participants to receive nicotine gum as part of a smoking cessation program and then tracked cancer outcomes over years of follow-up. In statistical models adjusted for other risk factors, nicotine replacement therapy was not a significant predictor of lung cancer. When NRT use and continued smoking were entered into the same model, smoking was clearly linked to lung cancer while NRT remained nonsignificant. The same held true for gastrointestinal cancers and for all cancers combined.¹

A UK study examining people who used NRT products long-term through stop-smoking services reached a similar conclusion: long-term NRT use was not associated with increased health risks, particularly compared to continued smoking.² These findings are reassuring, but there is an important caveat. Very long-term studies of NRT effects, the kind that would follow users for decades, do not yet exist. Some of the decision-making around NRT and cancer risk still relies on limited human data combined with what we know from laboratory experiments.³

Nicotine Is Not Classified as a Carcinogen

This is a point that surprises many people. The International Agency for Research on Cancer, the arm of the World Health Organization responsible for evaluating cancer-causing substances, has not included nicotine on its list of carcinogens.⁴ Tobacco smoke is absolutely classified as carcinogenic, but tobacco smoke contains thousands of chemicals beyond nicotine. The tar, polycyclic aromatic hydrocarbons, formaldehyde, benzene, and tobacco-specific nitrosamines in cigarette smoke are the primary cancer drivers. Nicotine is the addictive component, but addiction and carcinogenesis are different things.

That distinction matters for lozenges specifically. Unlike cigarettes or even smokeless tobacco, pharmaceutical-grade nicotine lozenges are manufactured to deliver nicotine without the combustion byproducts or the leaf-derived contaminants found in tobacco products.

What Is Actually Inside a Nicotine Lozenge

A chemical analysis comparing the contents of various nicotine and tobacco products found that NRT lozenges contained remarkably few harmful or potentially harmful constituents. In the lozenge product tested, the only compound detected above the quantification limit, apart from nicotine itself, was nickel at a very low level. No tobacco-specific nitrosamines were found. No polycyclic aromatic hydrocarbons were found either.⁵ By comparison, traditional smokeless tobacco products like moist snuff contained all of these compounds at much higher levels. Even nicotine gum, another NRT product, had a wider range of trace contaminants than the lozenge, though still far less than any tobacco product.

Biomarker studies in humans tell a consistent story. When researchers measured tobacco-specific nitrosamines and related compounds in the urine and saliva of NRT users, the levels were marginal and statistically indistinguishable from those of people who used no nicotine or tobacco at all.⁶ Smokers, by contrast, had the highest levels of every biomarker measured.

The Trace Nitrosamine Question

One finding that occasionally generates headlines deserves a closer look. Researchers have detected low levels of a carcinogenic compound called NNN (N′-nitrosonornicotine) in the urine of some people using oral NRT products like gum and lozenges. In about a third of the oral NRT users studied, NNN levels at one or more time points after quitting smoking were comparable to, or even higher than, their baseline levels while still smoking.⁷

How is this possible if the lozenges themselves contain no detectable nitrosamines? The answer is that the human body can convert nicotine into NNN through a process called endogenous nitrosation. When nicotine sits in your mouth, bacteria and other conditions in saliva can chemically transform a small portion of it into nornicotine, and then into NNN. A study of e-cigarette users, who also use nicotine without tobacco, found detectable NNN in their saliva, though at levels roughly six to seven times lower on average than in smokers.⁸

So any form of nicotine use, even a perfectly clean pharmaceutical product, can lead to some low-level formation of a known carcinogen in the body. The open question is whether those trace amounts are large enough to matter in practice. The human epidemiological data so far suggest they are not, but this is an area where researchers are honest about the gaps.

What Nicotine Does to Cells in the Lab

The reason the cancer question keeps coming up, despite the reassuring human data, is that nicotine does some troubling things in laboratory experiments. These findings do not mean lozenges cause cancer, but they explain why scientists have not entirely closed the book.

Nicotine can cause DNA damage. When human white blood cells were exposed to nicotine at concentrations of 1 and 10 micromolar, DNA damage increased significantly in a dose-dependent fashion. Interestingly, at a very low concentration comparable to what is found in the blood of habitual smokers, the effect reversed: DNA damage was actually lower than in untreated control cells.⁹ A similar pattern showed up in human nasal and airway cells, where significant DNA damage appeared only at relatively high concentrations, and the damage appeared to be driven by oxidative stress.¹⁰ Animal studies have confirmed nicotine’s ability to cause chromosomal damage in mice, and found that pretreatment with vitamin C strongly protected against it, further supporting the idea that oxidative mechanisms are involved.¹¹

Nicotine also promotes the growth of new blood vessels, a process tumors rely on to feed themselves. In laboratory models, nicotine and its major metabolite cotinine increased the production of vascular endothelial growth factor (VEGF), a protein that stimulates blood vessel formation, in endothelial cells at concentrations typical of what habitual smokers have in their blood.¹² In gastric cancer cells, nicotine stimulated both tumor cell proliferation and tumor-associated blood vessel formation through a pathway involving VEGF and an enzyme called COX-2.¹³

These lab findings describe what nicotine can do when applied directly to cells or tumors, often at concentrations higher than what a lozenge user would experience. The leap from “promotes tumor blood vessel growth in a lab dish” to “causes cancer in a person using lozenges” is a large one. But these mechanisms are the reason pharmacologists have not simply declared the matter closed.

A Concern for People Already Diagnosed With Cancer

The evidence around nicotine and existing cancer is arguably more worrying than the evidence around nicotine and cancer initiation. Multiple lab studies have found that nicotine can make cancer cells more resistant to chemotherapy. In lung cancer cells, nicotine prevented chemotherapy drugs from triggering the cell-death process they are designed to activate, improved cancer cell survival, and modestly increased DNA synthesis in those cells.¹⁴ The same pattern has appeared in bladder cancer, where nicotine exposure promoted tumor growth both in the lab and in living animals and weakened the ability of a common platinum-based chemotherapy drug to inhibit cancer cell growth.¹⁵

In small cell lung cancer specifically, researchers found that nicotine and cotinine at physiologically relevant concentrations reduced the ability of platinum-based chemotherapy drugs to damage cancer DNA, effectively accelerating the development of treatment resistance.¹⁶ This is a genuine clinical concern. If you are undergoing cancer treatment, any source of nicotine, including lozenges, could theoretically interfere with how well your therapy works. The specific receptors involved are alpha-7 nicotinic acetylcholine receptors, which play a role in lung cancer cell proliferation and metastasis and are a subject of active research as potential drug targets.¹⁷

This does not mean a cancer patient should keep smoking instead of switching to lozenges. Cigarette smoke delivers nicotine plus thousands of additional toxic and carcinogenic compounds. But it does mean that for people in active cancer treatment, the safest path is probably to work toward complete nicotine cessation rather than indefinite NRT use, and to discuss the specifics with their oncologist.

How Nicotine Affects the Immune System’s Cancer Surveillance

Your immune system is constantly scanning for and destroying abnormal cells before they grow into tumors. Natural killer cells are a key part of that defense. In a large cohort study, current smokers had measurably lower NK cell activity than both never-smokers and former smokers. NK cell activity also decreased in a linear fashion as cotinine levels (a marker of nicotine exposure) rose.¹⁸

Because cotinine is a product of nicotine metabolism regardless of the source, this raises the question of whether nicotine from lozenges could suppress NK cell activity in the same way. Animal research suggests it might. In a mouse model of lung metastasis, nicotine exposure impaired the ability of NK cells to kill cancer cells and release the chemical signals they use to coordinate an immune response. When the specific nicotine receptor involved was knocked out genetically, the suppressive effect largely disappeared.¹⁹ A broader review of nicotine’s immune effects found that by activating certain receptors on immune cells, nicotine can suppress the release of inflammatory signals in ways that increase blood vessel growth, promote metastasis, and enhance tumor cell survival.²⁰

Again, these are mechanistic findings. Nobody has shown that lozenge users have higher cancer rates because of suppressed NK cell activity. But the biology is plausible enough that researchers keep studying it.

Epigenetic Changes and Pancreatic Cancer

Beyond direct DNA damage, nicotine may also influence cancer risk through epigenetic changes, which are modifications to how genes are read without altering the DNA sequence itself. In human pancreatic duct cells, chronic exposure to nicotine caused a specific gene promoter to become hypermethylated, effectively silencing a gene involved in producing an inhibitory neurotransmitter. The researchers proposed this as a potential mechanism by which nicotine could contribute to pancreatic cancer development.²¹ This is early-stage science and far from proven in humans, but the pancreas is an organ where the epidemiological picture deserves watching.

Effects on the Mouth Itself

Because lozenges dissolve in your mouth, some people worry about local effects on oral tissue. A clinical study of sublingual nicotine tablets found that while some users developed lesions on the floor of the mouth during the first six weeks of treatment, all of them resolved by the six-month follow-up. Local symptoms were mild and tolerable, and the researchers concluded the product appeared safe for oral use.²²

That said, chronic overuse of NRT products has been linked to oral hyperkeratotic lesions, a thickening of the mouth’s lining. A case report documented this in a patient who had used nicotine replacement products excessively over a long period, noting that while the association is real, it is rarely reported in the literature.²³ Oral keratosis is not cancer, but it can resemble precancerous lesions visually and may warrant monitoring. A pilot study of nicotine pouch and e-cigarette users found that periodontal disease-associated bacteria were present in their saliva, suggesting that nicotine products could shift the oral microbiome in ways that affect gum health, though the study was preliminary and did not assess cancer outcomes.²⁴

Why Misperceptions About Lozenge Safety Are Themselves a Health Problem

Here is where the conversation gets genuinely frustrating from a public health standpoint. About two-thirds of smokers and ex-smokers in one large survey either agreed that nicotine replacement products are “just as harmful as cigarettes” or were unsure whether that was true. People who held that belief were significantly less likely to have ever used NRT and less likely to consider using it in a future quit attempt. Among those who did use nicotine gum, safety concerns led them to use fewer pieces per day and to stop sooner, both of which undermine the product’s effectiveness as a cessation tool.²⁵

This matters because while oral NRT is not risk-free in a theoretical sense, it is indisputably safer than continuing to smoke. Qualitative research with long-term NRT users has echoed this gap between perception and reality: many consumers are uncertain about whether their NRT use is safe, and current public health messaging does not always give them clear answers.²⁶ The irony is that fear of a speculative cancer risk from lozenges keeps people on a product, cigarettes, with a confirmed and massive cancer risk.

Nicotine Lozenges in the Broader Harm Reduction Landscape

The harm reduction framing is where current expert opinion has broadly settled. Nicotine lozenges sit at the cleanest end of the nicotine product spectrum. They contain no tobacco leaf, no combustion products, and vanishingly few of the harmful constituents found in cigarettes, smokeless tobacco, or even some newer nicotine pouch products. A recent review of oral nicotine products and oral cancer risk concluded that integrating harm reduction approaches with established prevention strategies could help reduce cancer risk for people who smoke or use high-risk smokeless tobacco, but emphasized that the current evidence requires cautious interpretation and ongoing monitoring of emerging products.²⁷

The practical upshot for most people is this: if you are using nicotine lozenges to quit smoking, the weight of current evidence strongly favors continuing. If you are using them indefinitely because you cannot stop, that is still vastly better than going back to cigarettes. And if you are a never-smoker considering nicotine lozenges for some other reason, the risk-benefit math is different and far less favorable, because you are adding a biologically active substance with known cellular effects and no corresponding benefit of removing tobacco exposure. The science here is not settled in the way that, say, the link between smoking and lung cancer is settled. But the evidence we do have points consistently in the same direction: lozenges are not clean in an absolute sense, but they are clean enough that worrying about them while smoking a pack a day is focusing on the wrong problem entirely.