Federal approvals of new drugs last year sank to the lowest level in five years, a drop-off some industry analysts attribute to more cautious regulators and fewer innovations from drugmakers.

The Food and Drug Administration last year approved 17 new molecular entities. Those are active ingredients that have never been marketed in the U.S. before.

The last year the FDA approved so small a number was 2002 and before that 1983, says Ira Loss of research firm Washington Analysis.

The FDA also approved 65 original new drug applications last year, the lowest number since 1999, according to data from BioMed Tracker of Sagient Research Systems. New drug applications include new molecular entities as well as new formulations or new manufacturers of existing drugs.

The FDA approved 64 percent of the applications it decided last year, down from 73 percent the year before, BioMed data shows.

Industry analysts say the FDA is more cautious in approving drugs after drawing criticism in recent years for approving some whose risks were found to outweigh their benefits after they went on the market.

Examples include painkillers Vioxx and Bextra, and an irritable bowel syndrome drug, Zelnorm. All are now off the market.

"It appears from the outside that the hurdles have been raised," says Michael Levesque, pharmaceutical analyst with Moody's Investors Service.

The FDA may be less likely to approve new drugs that lack clear advantages over older treatments and may carry unknown risks, adds Linda Bannister, health-care analyst with Edward Jones.

Drugs that hit FDA roadblocks last year included diet drug Acomplia, also known as Zimulti in the U.S. While pegged a potential blockbuster by industry analysts, an FDA panel in June recommended against its approval due to concerns it increases the risk of suicidal thoughts in patients. Sanofi-Aventis, the drug's maker, then withdrew the application.

Potential approvals for depression drug Pristiq and schizophrenia drug bifeprunox were both delayed after the FDA asked for additional data, says Levesque.

The FDA's standards for approving drugs are no different than in the past, says spokesman Christopher DeFrancesco. He says the rate of approvals to submissions remained steady at about 80 percent from 1997 through 2005.

Loss says the drug industry's "research drought" has led to weaker new-drug applications, thus fewer approvals. An explosion of drug discoveries started in the late 1980s, peaked in the mid-1990s and then "petered out," he says, despite more research spending by industry. In fiscal year 1996, the FDA approved 46 new molecular entities, FDA data shows.