No evidence suggests that Pfizer’s smoking cessation medication Chantix increases the risk of cancer; recall of this product is irrelevant to the safety of COVID-19 vaccines
The recall of Chantix, a smoking cessation aid developed by Pfizer, wasn’t related to the actual ingredients in the product. The company took this precautionary measure after finding nitrosamine impurities that exceeded the recommended limits in certain batches of the drug. Although some nitrosamines compounds may increase cancer risk in humans, there is no evidence that the particular one found in Chantix poses a health risk.
Lacks context: Nitrosamines aren’t actual ingredients in Chantix. The presence of nitrosamines in Chantix was due to contamination of certain batches of the drug. There is no evidence that the particular nitrosamine found in Chantix increases the risk of cancer in humans.
Flawed reasoning: The fact that Pfizer recalled one of its approved products doesn’t imply that other products from Pfizer are unsafe. Data from clinical trials and real-world studies in millions of people show that COVID-19 vaccines are very safe and effective against the disease.
Misinformation discouraging COVID-19 vaccination has taken many forms. One of them involves misleading claims suggesting that COVID-19 vaccine manufacturers marketed unsafe products in the past. These narratives foster distrust in the products from these manufacturers, including COVID-19 vaccines, as well as in public regulators.
In mid-September 2021, one claim adopting this approach took advantage of a nationwide recall on 16 July 2021 related to Chantix, a medication developed by Pfizer that acts as a smoking cessation aid. The company voluntarily recalled twelve lots of this product after detecting a potential carcinogenic compound at levels that exceeded the limits recommended by the U.S. Food and Drug Administration (FDA). On 16 September 2021, Pfizer expanded the recall to include all lots of Chantix tablets. As announced by the FDA:
“Pfizer is voluntarily recalling all lots of Chantix 0.5 mg and 1 mg Tablets to the patient (consumer/user) level due to the presence of a nitrosamine, N-nitroso-varenicline, at or above the FDA interim acceptable intake limit. As alternative suppliers have been approved in the United States, Pfizer is undertaking this precautionary measure.”
Some social media users interpreted this recall as evidence that clinical research and FDA approval don’t guarantee the long-term safety of medicines, including COVID-19 vaccines. Posts and memes making similar claims received more than 27,000 interactions on Facebook (examples here and here), Instagram, Twitter, and Reddit, according to the social media analytics tool Crowd Tangle.
However, using Pfizer’s recall to question the safety of its other medical products like COVID-19 vaccines is misleading, as we will explain below.
Chantix—which has the generic name of varenicline— is a prescription medicine to help adults stop smoking. The drug has been on the U.S. market since the FDA approved it on 10 May 2006. In June 2021, Pfizer detected higher than recommended levels of the nitrosamine N-nitroso-varenicline in some batches of the product, which prompted the company to undertake a voluntary recall.
Nitrosamines are a group of compounds that can occasionally form as chemical by-products. They are present in tobacco smoke and can also appear at low levels in drinking water and some foods, such as cured and grilled meats, dairy products, and vegetables. Occasionally, nitrosamine impurities can also appear in medicines. This can be due to contamination during the manufacturing process or due to storage and packaging conditions.
Several scientific studies found that exposure to high levels of some nitrosamines can cause cancer in laboratory animals[1-3]. For this reason, the International Agency for Research on Cancer classified nitrosamines as probable or possible carcinogens in humans. Because of their theoretical carcinogenic potential, the International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use (ICH) refers to all nitrosamine compounds as a “cohort of concern” in its guidelines for the industry. Likewise, the FDA regularly monitors nitrosamine levels in medicines and issues guidance for drug manufacturers to detect and prevent nitrosamine impurities in their products.
According to FDA laboratory analyses, some lots of Chantix tablets contained N-nitroso-varenicline in levels ranging from 150 to 470 nanograms per pill, well above the FDA’s recommended limit of 37 nanograms per day.
Some Facebook memes claimed that “it took 15 years to uncover” the danger posed by Chantix, implying that clinical research and approval don’t guarantee the long-term safety of medical products. Making such a claim based on Pfizer’s recall is incorrect because the presence of nitrosamines in certain batches of the drug doesn’t mean that Chantix itself contains dangerous ingredients. Instead, it was due to contamination of some batches of the product that were manufactured around the same time. Specifically, Pfizer recalled those lots with expiration dates between August 2021 and December 2023.
In addition, posts suggesting that Chantix inherently contains carcinogens or causes cancer are misleading for several reasons.
First, the particular nitrosamine found in Chantix was N-nitroso-varenicline. This compound has no records of harmful effects in animals or humans. Due to the lack of data, the FDA doesn’t calculate the limit of 37 nanograms per day based on the specific risk of N-nitroso-varenicline, which is unknown, but on the “information available on closely related nitrosamine compounds”.
Second, the acceptable intake limit for nitrosamines is based on lifetime exposure, meaning 37 nanograms of N-nitroso-varenicline every day for 70 years. However, the duration of Chantix treatment is generally limited to 12 weeks, up to a maximum of six months. Even if N-nitroso-varenicline were a confirmed carcinogen, the risk that such a limited exposure could cause cancer in humans is very low. The FDA explains:
“N-nitroso-varenicline may be associated with a potential increased cancer risk in humans, but there is no immediate risk to patients taking this medication. An increased cancer risk would be associated with long-term use, and the health benefits of stopping smoking outweigh the cancer risk from the nitrosamine impurity in varenicline.”
Apart from the fact that Chantix isn’t itself associated with an increased risk of cancer, Pfizer’s recall of one of its approved drugs doesn’t imply that other products from Pfizer are potentially unsafe. This argument is incorrect because it doesn’t consider the vast majority of products that Pfizer didn’t recall, including COVID-19 vaccines.
Before receiving Emergency Use Authorization by the FDA, COVID-19 vaccines had to demonstrate that they were safe and effective in large clinical trials, as Health Feedback explained in this review. As of 4 November 2021, about half of the world population has received at least one dose of a COVID-19 vaccine. In such a large population, the majority of the vaccine side effects have likely emerged already. Common side effects of COVID-19 vaccines are mild and short-lived and, while serious side effects can occur, they are very rare. As Health Feedback explained in this article review, long-term side effects are also very unlikely and most of the side effects of vaccination occur within six weeks. Therefore, the potential risks of COVID-19 vaccines are much smaller than the benefits of vaccination.
In summary, claims suggesting that Pfizer’s products, including COVID-19 vaccines, can’t be trusted based on the company’s recall of one product are misleading. While some batches of Chantix tablets contained potential carcinogens in levels exceeding the recommended limits, they are unlikely to pose a health threat. Pfizer’s recall was only a voluntary preventive measure.
The particular nitrosamine detected in Chantix tablets hasn’t proven dangerous for human health. Furthermore, its presence wasn’t because nitrosamines are actual ingredients for Chantix, but because certain batches of the drug were contaminated. Therefore, Pfizer’s recall of Chantix doesn’t call into question the capacity of manufacturers and regulatory agencies to guarantee the safety of other medical products, including COVID-19 vaccines, which have proven very safe.
- 1 – Peto et al. (1991) Dose and Time Relationships for Tumor Induction in the Liver and Esophagus of 4080 Inbred Rats by Chronic Ingestion of N-Nitrosodiethylamine or N-Nitrosodimethylamine. Cancer Research.
- 2 – Encell et al. (1996) The relationship between N -nitrosodimethylamine metabolism and DNA methylation in isolated rat hepatocytes. Carcinogenesis.
- 3 – Rudel et al. (2007) Chemicals causing mammary gland tumors in animals signal new directions for epidemiology, chemicals testing, and risk assessment for breast cancer prevention. Cancer.