Twenty percent of all new drugs are found to have serious or life-threatening effects unknown or undisclosed at the time of drug approval, according to a study published in the Journal of the American Medical Association (JAMA).

The study, by researchers at Harvard Medical School and Public Citizen, a nonprofit consumer advocacy organization, found that half of these serious adverse effects are detected within seven years after a drug is first introduced onto the market. Damage to the liver, heart and bone marrow, as well as pregnancy risks, are the most common problems that arise after new drugs are introduced.

Sixteen drugs were withdrawn from the market over the 25-year study period, half of those withdrawals taking place within two years of a drug's introduction.

The study also analyzed drug entries in the "Physicians' Desk Reference" (PDR), the most common source of drug information for doctors. The authors examined 26 volumes of the "PDR," from 1975-2000, to determine how many drugs were found to have new serious adverse effects that were not known when the drug was first released. The study authors found that the estimated probability of acquiring a new black box warning or being withdrawn from the market over 25 years was 20 percent.

"This study will change the way I talk to patients about the use of new drugs," said Dr. Karen Lasser, study author and primary care doctor and researcher at Cambridge Hospital and Harvard Medical School. "If there is a safer, effective drug that has been in use for a number of years, I would strongly recommend it over a newer drug whose safety profile is unknown. I would prescribe a new drug only when absolutely necessary, and then watch for adverse effects very, very closely."

Prescription drug adverse effects are a major public health problem.

"Twenty million patients, almost 10 percent of the U.S. population, were exposed to the five drugs withdrawn from the market between September 1997 and September 1998," said Dr. Paul Allen, study co-author, an internal medicine specialist at Cambridge Hospital and Harvard Medical School. "Yet the drug companies push the public and doctors to use new drugs that are more profitable but also more dangerous."

The authors recommend that the U.S. Food and Drug Administration (FDA) not approve new drugs that are found to have safety problems in pre-marketing trials, especially when safer, equally effective therapies already exist, or when a new drug treats a benign condition.

"For many years, we have recommended to doctors and patients not to use new drugs until they have been on the market for at least five years, unless the drug is an important advance over existing treatments, which is rarely the case," said Dr. Sidney Wolfe, director of Public Citizen's Health Research Group and study co-author. "This study provides much more extensive evidence for this cautious approach to treating patients."

The other study authors (Drs. Steffie Woolhandler, David Himmelstein and David Bor) are associate professors of medicine at Harvard Medical School.