WASHINGTON (Reuters) - U.S. regulators on Thursday listed two dozen drugs, including weight-loss medicines and sleep disorder pills, that it is at an early stage of reviewing for potential safety problems.

View of pills manufactured on a production line in a pharmaceutical company. REUTERS/Jacky Naegelen

Many of the issues have been previously disclosed, but remain under review by the Food and Drug Administration.

The FDA said it was checking Pfizer Inc’s smoking cessation drug Chantix for possible risk of accidental injury, vision impairment and other issues, and Cephalon Inc’s sleep disorder drugs Nuvigil and Provigil for a potential of serious skin reactions.

Other drugs listed included orlistat, a weight-loss drug sold by Roche Inc as the prescription product Xenical and by GlaxoSmithKline Plc as the over-the-counter drug Alli. The FDA said it was continuing to evaluate liver toxicity reports for orlistat.

The FDA also said Pfizer’s overactive bladder drug Detrol was under investigation for reports of Stevens-Johnson syndrome, a serious skin reaction.

The FDA releases a quarterly list of safety probes as part of an effort to inform the public about early investigations of potential side effects that have been reported. The list released on Thursday covers October through December 2008.

The problems are potential safety issues and their appearance on the list “does not mean that FDA has identified a causal relationship” with the drug, the agency said.

Roche spokesman Terry Hurley, commenting on the listing of Xenical, said available data “does not suggest that orlistat is causally related” to liver problems, noting obesity itself is a risk factor for liver injury.

Glaxo spokeswoman Mary Anne Rhyne also said “no causal relationship ... has been established” between Alli and hepatitis, a liver disease.

Pfizer spokeswoman Sally Beatty said the maker of Chantix evaluates any reports of health problems and “as with all our medicines, we work with the FDA to ensure our labeling reflects the latest safety information.”

The FDA had said last year it was taking a closer look at Chantix after reports of accidents, vision loss and other problems in hundreds of patients

A Cephalon spokeswoman did not immediately respond to a request for comment on Nuvigil and Provigil. Serious skin reactions were identified as an issue with the drugs in 2007 and the FDA continues to study the matter, the agency said.

A spokeswoman for Glaxo could not immediately be reached for comment on the listing of Alli.

Bristol-Myers Squibb Co’s HIV drug, Sustiva, was listed due to one report of an eye-related birth defect. A description of the case was added to the drug’s prescribing instructions in March 2009, the FDA said.

Bristol-Myers spokeswoman Cristi Barnett said the drug’s label states it should only be used in pregnant women, “if the benefit to the patient justifies the potential risk to the fetus.”

The FDA also is probing pancreatitis with Bayer AG's contraceptive Yasmin, the agency's list said. Bayer spokeswoman Rose Talarico said the listing "was not prompted by any change in the existing safety profile" of Yasmin and the company "continues to work with the FDA to ensure that the most up-to-date and accurate safety information" is included in the drug's label. The FDA posted the list on its Websitehere.