The removal of varenicline from the UK market in 2021 after impurities were found in supplies may have led to thousands fewer people attempting to stop smoking, researchers have estimated.

Varenicline (Champix) is not available in the UK after Pfizer paused distribution in 2021 due to high levels of potentially carcinogenic nitrosamines detected in the tablets. Medicines regulators later recalled batches of the medicine.

An analysis by researchers by University College London showed before this, the drug had once been used in around 4% of quit attempts.

With smokers moving to less effective smoking cessation therapies or not using any medication or nicotine replacement to help them quit, they estimated that 4,200 fewer people would have quit the habit for good over the course of a year.

In the longer term this could lead to 1,890 more smoking deaths for each year varenicline was unavailable, they reported in the journal Addiction.

Data for the analysis was taken from the Smoking Toolkit Study which showed that by the second half of 2022, varenicline use fell to 0.8% of all quit attempts with no one using it in the last quarter of the year.

This was backed up by data from GP surgeries in England which suggested varenicline accounted for just 0.1% of smoking cessation prescriptions in December 2022.

The researchers noted that while some smokers moved to using prescription drug bupropion or NRT, these are estimated to be around 40% less effective than varenicline at helping people successfully quit.

Their data highlighted that while prescriptions for bupropion doubled between July 2021 and December 2022, there was also a 35% drop in monthly prescriptions for smoking cessation medicines overall.

Generic versions of varenicline have been made available in the US, Canada and Australia but not in the UK.

The team also calculated that if nitrosamines in varenicline tablets were similarly carcinogenic to tobacco-specific nitrosamines, a standard 12-week course would give an equivalent dose to 18 days of smoking 11 cigarettes a day – much lower level of risk than continuing to smoke in the long term.

Distribution of bupropion had also been paused for a period in 2022/23 after European medicines regulators called for a review of nitrosamine contamination. It is not known if varenicline will become available in the UK again.

Another effective treatment, cytisine, was launched in the UK at the start of this year and could fill the gap left by varenicline as long as people are aware it is an option, the researchers added.

A Cochrane review last year found that cytisine and varenicline were among the most effective tools for helping people stop smoking but were not widely available.

Study lead Dr Sarah Jackson, from the UCL Tobacco and Alcohol Research Group, said varenicline is a ‘gold-standard prescription treatment’ for smokers trying to quit.

‘The disruption of its supply in the UK and Europe likely reduced the number of people successfully stopping smoking, which will lead to more preventable deaths. Our study gives a sense of the scale of this.’

She added: ‘Efforts to promote awareness of cytisine among smokers and prescribers may help to reduce smoking deaths over the long term.’

Senior author Professor Lion Shahab, also from the UCL Tobacco and Alcohol Research Group, pointed out that the withdrawal of varenicline had had substantial unintended consequences.

‘Industry and regulators acted with caution, leading to a life-saving smoking cessation medicine becoming unavailable.

‘Perhaps they did not fully consider the effects this would have on the health of continuing smokers, who are exposed to a much higher level of risk than that likely caused by nitrosamine impurities in varenicline.’

This article first appeared on our sister title Pulse.