FDA is warning patients about a potential mix-up between powerful prescription pain drugs and common OTC medications like Excedrin and Gas-X manufactured by Swiss drug maker Novartis.

The issue is a result of major manufacturing problems at a Lincoln, Nebraska, facility which was shut down last month because of the issues.

Novartis has recalled bottles of Excedrin, Bufferin, Gas-X and NoDoz which may have included mixed up pills.

Now the Food and Drug Administration says some of those OTC pills may have accidentally been packaged with powerful prescription painkillers made at the same facility.

The opioid drugs are sold by Endo Pharmaceuticals as Percocet, Endocet, Opana and Zydone.

FDA officials say they are not recalling the prescription drugs because they are medically necessary and the likelihood that they contain stray pills is low.

FDA’s Dr. Edward Cox told reporters:

“The likelihood of finding a wrong tablet in an opiate pain medication dispensed to patients is low and patients should not be unduly alarmed.”

Novartis said it has voluntarily suspended operations and shipments from its Lincoln, Nebraska, facility to rectify the problems at the site.

The plant has been under fire from inspectors from FDA for its quality control. An FDA report said the company did not properly address any of the 223 critical complaints it received in 2011.

In 2010, the plant did not rectify 165 of the 587 complaints it got, according to the FDA.

Additionally, the company failed to investigate 166 reports of pills being packaged in the wrong bottles in 2009.

The Journal Star newspaper in Lincoln reported that the FDA blamed the problems on Novartis having too few people at the plant to review complaints. The staffers the company does have are poorly trained, the FDA, added.

Novartis said it is working to upgrade and improve manufacturing and training at the Nebraska plant before restarting production.

Company officials have said they don’t know exactly how many bottles will be affected by the recall or when the factory will come back online.

Spokeswoman Julie Masow said there is no indication prescription pills actually got mixed up with Novaris OTC drugs, but the recalls are a precaution.

Novartis said its Consumer Health unit will take a one-time charge currently estimated at $120 million in the fourth quarter relating to the recalls and improvements at the facility.

The company said it implemented the recall, which affects U.S. retailers, voluntarily and is working with FDA during the process.

It became aware of the potential problem during an internal review that identified broken and chipped pills, and inconsistent bottle packaging that could cause pills to be mixed up.

Novartis said it wanted to make sure that customers didn’t take any pills that they might be allergic to or that might become dangerous when mixed with their other medications, though it also said that there have been no such reports from consumers.

The drug maker said that some of the bottles of headache medicine Excedrin and caffeine caplets NoDoz with expiration dates of December 20, 2014, or earlier will be subject to the recall.

Some of the packages of pain medicine Bufferin and stomach medicine Gas-X with expiration dates of December 20, 2013, or earlier will also be affected.

The company said it will post more information Monday at www.novartisOTC.com. Customers can also call the company at 1-888-477-2403 Monday to Friday, 9:00 a.m. to 8:00 p.m. EST.