US regulators have posted their first quarterly report which lists 20 drugs that are being evaluated for potential safety issues but they are stressing that it does not mean the therapy necessarily carries that risk.

The US Food and Drug Administration says the medicines have been identified based on a review of reports from its Adverse Event Reporting System. These include Eli Lilly's antidepressant Cymbalta (duloxetine) which is being investigated for links to urinary retention, Biogen Idec and Elan Corp's multiple sclerosis drug Tysabri (natalizumab) for skin melanomas and GlaxoSmithKline's oncology agent Tykerb (lapatinib) which is being investigated for hepatotoxicity.

The full list which also includes AstraZeneca’s Seroquel (quetiapine) for overdose due to sample pack labelling confusion, has been published on the FDA website. The list is being provided under provisions of the FDA Amendments Act, signed last September, which requires that the agency inform the public each quarter of new safety information or potential signals of serious risk,

The appearance of a therapy on this list does not mean that the FDA has identified a causal relationship between the drug and the risk. Janet Woodcock, director of the agency’s Center for Drug Evaluation and Research, said: "My message to patients is this: Don't stop taking your medicine. If your doctor has prescribed a drug that appears on this list, you should continue taking it unless your doctor advises you differently."

She added that over the past two years, the FDA “has become much more proactive in our communication about possible safety problems”. Patients and health care professionals have told the agency they want to be informed about such risks sooner and “they want to know when the FDA is in the early stages of looking into a potential safety problem”.

The response to the list has been cautious. Thomas Moore at the Institute for Safe Medication Practices told the Associated Press “it's a good thing to get started but it needs to have much more detail if it's to have significant safety value. A table with just a few words of description is quite limited."

The Pharmaceutical Research and Manufacturers of America’s Alan Goldhammer said the organisation backs the idea of giving more safety information to doctors and patients, but it fears that it could lead to alarmism. "Our reservation is that patients will be abruptly stopping therapy," he said, and “one can't generalise with an emerging safety notice. It may affect half the patients, a quarter of the patients, or only a small subset of the patients”.