Pfizer Inc said recently that it is pausing the distribution of its anti-smoking treatment, Chantix, after finding elevated levels of cancer-causing agents called nitrosamines in the pills.

The drugmaker is recalling a number of anti-smoking drugs. The US drug regulator has, in the past, reached out to companies whose drugs had N-nitrosodimethylamine (NDMA) over accepted levels.

The US Food and Drug Administration (FDA) last year found high levels of NDMA in some versions of the popular diabetes drug metformin. NDMA contamination was responsible for the recall of the heartburn drug Zantac sold by Sanofi SA in 2019.

Chantix was approved by the FDA in May 2006 as a prescription medication that, along with support, helps adults aged 18 and over quit smoking and is used for 12 to 24 weeks.

Pfizer said the pause in distribution is out of an abundance of caution and pending further testing.

“The benefits of Chantix outweigh the very low potential risks, if any, posed by nitrosamine exposure from varenicline on top of other common sources over a lifetime,” Pfizer spokesperson Steven Danehy said in an email to Reuters.