Pfizer is expanding the recall of its anti-smoking drug Chantix (varenicline), the company announced Friday.

The nationwide recall of all Chantix 0.5 mg and 1 mg tablets was prompted because they may contain levels of a nitrosamine, N-nitroso-varenicline, that are at or above levels approved by the U.S. Food and Drug Administration.

Long-term ingestion of N-nitroso-varenicline may be linked to a "theoretical potential increased cancer risk in humans," the company said, adding that no immediate risk to patients taking Chantix exists.

"The health benefits of stopping smoking outweigh the theoretical potential cancer risk from the nitrosamine impurity in varenicline," Pfizer said in its statement.

Nitrosamines are common in water and foods — including cured and grilled meats, dairy products and vegetables — so everyone is exposed to some level of these chemicals.

Patients taking Chantix should consult with their doctor about other treatment options. So far, Pfizer has received no reports of adverse events tied to this recall, the company stated.