Litigation Guides

Chantix Recall & Cancer Risk

Chantix contains N-nitroso-varenicline, one of the four nitrosamine contaminants involved in the US FDA recall announcements. There are proposed mechanisms of action for how N-nitroso-varenicline may increase the risk of cancer. While there is strong evidence that other nitrosamines increase cancer risk, further research is needed to confirm that Chantix use contaminated with N-nitroso-varenicline increases the risk of cancer.

Medically Reviewed



February 2006: The U.S. Food and Drug Administration (FDA) granted Varenicline a "priority review" designation. This designation shortened the standard ten-month review period to six months. The expedited review was based on Varenicline's proven effectiveness in clinical trials and the absence of apparent safety concerns identified at that time.1

May 2006: Pfizer receives FDA approval for the use of Chantix (varenicline) 0.5 mg and 1 mg Tablets as an aid to smoking cessation treatment.2,3

April 2016: Pfizer published the results of a large-scale clinical trial known as the Evaluating Adverse Events in a Global Smoking Cessation Study (EAGLES). This study assessed the safety profile of varenicline, specifically focusing on neuropsychiatric side effects. The EAGLES trial demonstrated that varenicline use did not lead to a significant increase in such adverse events compared to either nicotine replacement therapy or a placebo.4

December 2016: The FDA removed the strongest safety warning ("black box warning") from varenicline (Chantix) labeling. This decision followed a comprehensive review, including the April 2016 EAGLES study, which showed that the benefits of varenicline in smoking cessation outweighed the risks. However, the FDA emphasized continued caution regarding potential neuropsychiatric side effects (depression, suicidal behavior), particularly for individuals with a history of mental illness or current treatment of mental health disorders.5

September 2020: Continuing concerns about nitrosamine impurities in medications (e.g., metformin, a diabetes medication, and ranitidine, a heartburn medication) prompted the FDA to set an acceptable daily intake limit (AI) for varenicline nitrosamine impurities at 37 nanograms.6 This limit factored in the estimated increased cancer risk of 1 in 100,000 individuals taking a drug at that AI or higher for 70 years.

June 2021: Pfizer paused distribution of Chantix worldwide.7

July 2021: Pfizer initiated a voluntary recall of twelve lots of Chantix tablets (various strengths) at the consumer level due to elevated levels of N-nitroso-varenicline, a nitrosamine impurity, exceeding Pfizer's internal safety limit.8 The FDA subsequently alerted healthcare professionals and patients about the recall, highlighting the nine originally reported lots recalled by Pfizer.9

August 2021: FDA testing revealed N-nitroso-varenicline levels exceeding 150-470 nanograms per tablet in certain tested Chantix lots. Pfizer, in response, initiated a voluntary consumer-level recall of an additional four Chantix lots due to these elevated nitrosamine levels exceeding their established safety threshold.10

September 2021: Pfizer significantly expanded its voluntary consumer-level recall of Chantix (varenicline) tablets. This included all remaining lots of both 0.5mg and 1mg strengths. The reason for the expanded recall was the presence of N-nitroso-varenicline at levels meeting or exceeding the FDA's interim acceptable intake limit.11

Chantix box with cigarette

What is Chantix?

Varenicline is a medication used to help people quit smoking. Its mechanism of action and discovery are described below:

  • Nicotine Addiction: Nicotine's addictive properties are linked to its interaction with specific brain cell receptors (called nicotinic acetylcholine receptors, or nAChRs), particularly the α4β2 subtype.12,13 A cell receptor is like a lock on the surface of a cell that only certain keys, like natural chemical messengers or drugs, can bind to, triggering a change inside the cell.
  • Dopamine and Reward: Nicotine activation of these receptors leads to release of dopamine, a neurotransmitter associated with reward, making smoking pleasurable.14,15
  • Withdrawal and Cravings: During smoking cessation, low dopamine levels trigger cravings and withdrawal symptoms.16,17
  • Varenicline's Role: Varenicline acts as a partial agonist at the α4β2 nAChRs. This means it partially activates the receptor, potentially mimicking some of nicotine's effects (like dopamine release) in a weaker way.
  • Theoretical Benefit: This partial activation might help counteract the low dopamine state during withdrawal, reducing cravings and withdrawal symptoms, thereby aiding smoking cessation.
  • Development of Varenicline: Inspired by the use of Cytisine, a plant-based partial agonist, researchers modified its structure to create varenicline, with improved potency and efficacy for smoking cessation.18,19,20,21,22
  • Varenicline Competitive Binding: Varenicline competes with nicotine for binding sites on the α4β2 nAChRs. This potentially prevents nicotine from fully activating the receptors and triggering the rewarding effects of smoking.22
  • Market Presence: Varenicline is marketed as Chantix (US) and Champix (EU) and has been prescribed frequently (over 1.8 million prescriptions).22,23

Chantix Contaminants

Identified nitrosamine impurities with carcinogenic (cancer-causing) potential include:

  • NDMA (N-Nitrosodimethylamine)
  • NDEA (N-Nitrodiethylamine)
  • NMBA (N-Nitrosomethylethylamine)
  • N-nitroso-varenicline

Sources of Exposure

Sources of nitrosamine impurities include: 6,24,25,26

  • NDMA: water treatment (chlorination/chloramination), cured meats, fish, beer, tobacco products, tobacco smoke (levels vary)
  • NDEA: found as an impurity in a class of blood pressure drugs known as Angiotensin II Receptor Blockers (ARBs), which act by relaxing blood vessels.
  • N-nitroso-varenicline: an impurity specific to Chantix

Carcinogenicity Classifications

Nitrosamines can be grouped by cancer risk, as follows:

  • NDMA and NDEA: These nitrosamines have been classified as probable human carcinogens by international agencies like the International Agency for Research on Cancer (IARC).27
  • NMBA: Animal studies in rats show tumor induction in the gastrointestinal tract and bladder at high doses.28,29
  • N-nitroso-varenicline: Carcinogenicity data is not yet available.

Human Studies on NDMA

Human studies demonstrating increased cancer risk posed by nitrosamine include the following:

  • European Prospective Investigation into Cancer and Nutrition (EPIC) Study: The EPIC study evaluated over 23,363 people aged 40-79. Researchers discovered that higher dietary intake of NDMA was associated with an elevated risk of colorectal cancer, after adjusting for other relevant factors.30
  • Canadian Case-Control Study: This study linked increased dietary NDMA intake to a higher risk of colorectal cancer.31

Liver Cancer and Association with NDMA and NDEA

Research suggests NDMA and NDEA may increase risk of liver cancer, as follows:

  • Human Study in Germany: Researchers found that NDMA-contaminated valsartan was associated with a slightly increased risk (1.16-fold) of liver cancer.32
  • Experimental Studies in Animals: NDEA used at high doses in mice induces liver tumors, potentially through DNA damage.33,34

Regulatory Limits and Recalls

FDA regulatory limits on nitrosamine contaminants led to the following recalls:

  • Recalls of Valsartan and Other ARB Medications: Impurities exceeding the FDA's interim acceptable intake limit (0.08 ppm) of NDEA led to recalls of the blood pressure medication, valsartan, and other ARB medications.26,35,36
  • Zantac (Ranitidine) Recall: Valisure detected concerning NDMA levels exceeding 300,000 nanograms (ng) per tablet when analyzing Zantac (ranitidine) at high temperatures, likely due to inherent instability of the ranitidine molecule.37 Opportunities for high-temperature exposure exist throughout the supply chain. This is significantly higher than the FDA's current acceptable daily intake limit of 96 ng for NDMA.38 These findings led to a recall of all ranitidine products in 2020.
  • Metformin Recall: Batches of metformin were voluntarily recalled by Viona Pharmaceuticals Inc. in 2022 due to the detection of NDMA impurity.39

Complications: Chantix and Cancer Risk

FDA Findings and Safety Limits

The FDA set safety limits on N-nitroso-varenicline found in Chantix, as follows:6

  • Testing: In August 2021, the FDA identified elevated levels of N-nitroso-varenicline (a nitrosamine impurity) in certain Chantix batches, ranging from 150-470 ng per tablet.
  • Daily Intake Limit: The FDA established a daily intake limit of 37 ng (18.5 ppm) of N-nitroso-varenicline, which was considered safe based on lifetime exposure modeling.

Higher Limits and Risk: Agency scientists determined that higher intake levels, up to 185 ng/day (92.5 ppm), pose a slightly increased cancer risk compared to the 37 ng/day limit.

N-Nitroso-Varenicline and Carcinogenicity

The cancer risk of N-nitroso-varenicline can be summarized as follows:

  • Proposed Mechanism: The potential carcinogenicity of N-nitroso-varenicline is linked to its metabolic activation. It's believed that cytochrome P450 enzymes convert N-nitroso-varenicline into alkyl diazonium ions, which can directly damage DNA through alkylation (adding unwanted chemical groups).40
  • Selective Tumor Induction: The varying distribution of these activating enzymes in different tissues may explain why nitrosamines like N-nitroso-varenicline might selectively cause tumors in specific organs.40

Alternative Mechanism: Nitrosamines may also disrupt cellular DNA repair processes, leading to mutations and potentially increasing cancer risk.41,42

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Does Chantix Cause Cancer?

Strength of available evidence: MODERATE

  • While nitrosamines are closely correlated with cancer development and a proposed mechanism of action for carcinogenic properties of N-nitroso-varenicline exists, further research is needed to confirm that Chantix use increases risk of cancer.

Works Cited


Kuehn, B. M. FDA speeds smoking cessation drug review. Jama 295, 614.


FDA. "FDA Approves Novel Medication for Smoking Cessation“. Press release (2006).,87.aspx


FDA. "Drug Approval Package: Chantix (Varenicline) NDA #021928".


Anthenelli, R. M. et al. Neuropsychiatric safety and efficacy of varenicline, bupropion,and nicotine patch in smokers with and without psychiatric disorders (EAGLES): a double-blind, randomised, placebo-controlled clinical trial. Lancet 387, 2507-2520.


FDA. FDA Drug Safety Communication: FDA revises description of mental health side effects of the stop-smoking medicines Chantix (varenicline) and Zyban (bupropion) to reflect clinical trial findings.


"Carcinogen Contamination Halts Sales of Smoking-Cessation Drug". (2021).


Pfizer. Pfizer Issues A Voluntary Nationwide Recall for Twelve Lots of CHANTIX® (varenicline) Tablets Due to N-Nitroso Varenicline Content. Press release (2021).


FDA. "FDA Updates and Press Announcements on Nitrosamine in in Varenicline". (2021).


Pfizer. Pfizer Expands Voluntary Nationwide Recall to include Four Additional Lots of CHANTIX® (varenicline) Tablets Due to N-Nitroso Varenicline Content. Press release (2021).



Picciotto, M. R. et al. Acetylcholine receptors containing the beta2 subunit are involved in the reinforcing properties of nicotine. Nature 391, 173-177.


Tapper, A. R. et al. Nicotine activation of alpha4* receptors: sufficient for reward, tolerance, and sensitization. Science 306, 1029-1032.


Di Chiara, G. Role of dopamine in the behavioural actions of nicotine related to addiction. European journal of pharmacology 393, 295-314.


Quinn, D. I., Wodak, A. & Day, R. O. Pharmacokinetic and pharmacodynamic principles of illicit drug use and treatment of illicit drug users. Clinical pharmacokinetics 33, 344-400.


Hughes, J. R., Higgins, S. T. & Bickel, W. K. Nicotine withdrawal versus other drug withdrawal syndromes: similarities and dissimilarities. Addiction 89, 1461-1470.


Malin, D. H. Nicotine dependence: studies with a laboratory model. Pharmacology, biochemistry, and behavior 70, 551-559,


Seeger, R. [Cytisine as an aid for smoking cessation]. Medizinische Monatsschrift fur Pharmazeuten 15, 20-21 (1992).


Prochaska, J. J., Das, S. & Benowitz, N. L. Cytisine, the world's oldest smoking cessation aid. BMJ 347, f5198, (2013).


Papke, R. L. & Heinemann, S. F. Partial agonist properties of cytisine on neuronal nicotinic receptors containing the beta 2 subunit. Molecular pharmacology 45, 142-149 (1994).


Scharfenberg, G., Benndorf, S. & Kempe, G. [Cytisine (Tabex) as a pharmaceutical aid in stopping smoking]. Das Deutsche Gesundheitswesen 26, 463-465 (1971).


Coe, J. W. et al. Varenicline: an alpha4beta2 nicotinic receptor partial agonist for smoking cessation. Journal of medicinal chemistry 48, 3474-3477, (2005).


Etter, J. F. Cytisine for smoking cessation: a literature review and a meta-analysis. Archives of internal medicine 166, 1553-1559, (2006).


Sedlak, D. L. et al. Sources and fate of nitrosodimethylamine and its precursors in municipal wastewater treatment plants. Water environment research : a research publication of the Water Environment Federation 77, 32-39.


Hecht, S. S. Biochemistry, biology, and carcinogenicity of tobacco-specific N-nitrosamines. Chemical research in toxicology 11, 559-603.


Ray, A., Atal, S. & Sadasivam, B. Understanding the molecular-pharmaceutical basis of sartan recalls focusing on valsartan. Global cardiology science & practice 2020, e202025.


OEHHA. Evidence on the Carcinogenicity of N-Nitrosomethyl-n-Alkylamines; OEHHA: Oakland, CA, USA.


Lijinsky, W., Reuber, M. D., Saavedra, J. E. & Singer, G. M. Carcinogenesis in F344 rats by N-nitrosomethyl-n-propylamine derivatives. Journal of the National Cancer Institute 70, 959-963.


Thomas, B. J., Kovatch, R. M. & Lijinsky, W. The induction of bladder tumors in F344 rats by intravesicular administration of some nitrosamines. Japanese journal of cancer research : Gann 79, 309-313.


Loh, Y. H. et al. N-Nitroso compounds and cancer incidence: the European Prospective Investigation into Cancer and Nutrition (EPIC)-Norfolk Study. The American journal of clinical nutrition 93, 1053-1061.


Zhu, Y. et al. Dietary N-nitroso compounds and risk of colorectal cancer: a case-control study in Newfoundland and Labrador and Ontario, Canada. The British journal of nutrition 111, 1109-1117.


Gomm, W. et al. N-Nitrosodimethylamine-Contaminated Valsartan and the Risk of Cancer-A Longitudinal Cohort Study Based on German Health Insurance Data. Deutsches Arzteblatt international 118, 357-362.


Shetty, S., Anushree, U., Kumar, R. & Bharati, S. Mitochondria-targeted antioxidant, mito-TEMPO mitigates initiation phase of N-Nitrosodiethylamine-induced hepatocarcinogenesis. Mitochondrion 58, 123-130.


National Center for Biotechnology Information. PubChem Compound Summary for CID 5921, N-Nitrosodiethylamine. Accessed Mar. 20, 2024.


FDA. FDA Announces Voluntary Recall of Several Medicines Containing Valsartan Following Detection of an Impurity.


FDA. FDA Updates and Press Announcements on Angiotensin II Receptor Blocker (ARB) Recalls (Valsartan, Losartan, and Irbesartan).


FDA. Laboratory analysis of ranitidine and nizatidine products.


FDA. Viona Pharmaceuticals Inc., Issues Voluntary Nationwide Recall of Metformin HCl Extended-Release Tablets, USP 750 mg, Due to the Detection of N-Nitrosodimethylamine (NDMA) Impurity.


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