In November the pharmaceutical company Perrigo recalled 11 million bottles of generic acetaminophen, sold under such store brands as CVS and Wal-Mart, after metal fragments were detected in a small number of caplets. No injuries were reported, and the Food and Drug Administration (FDA) said the probability of serious harm from the pills was remote. But the news left some consumers wondering: Are generic drugs safe?

Perrigo has had its share of problems, recalling 10 other products over the past year. Still, recalls are hardly limited to generics. In September 2005 the manufacturer of Tylenol Arthritis Extended Relief pulled some of its caplets from store shelves because some bottles may have contained broken metal. That same month Children's Tylenol Oral Suspension was recalled because some bottles may have contained pieces of wire.

Generic drugs save consumers an estimated $8 billion to $10 billion a year at the pharmacy, but how these products are regulated and brought to market is still a mystery to some. Here are some answers to consumer questions.

A generic drug is simply a copy of a brand-name medicine whose patent has expired. By law, a brand-name company loses its right to be the exclusive maker of a drug after a certain period, usually about 20 years. Companies that specialize in making and distributing generic versions of drugs then get the green light to manufacture and sell them. Much of the time the same company that makes a brand-name drug also makes its less expensive, generic version in order to sell to both markets.

Yes. You needn't worry that a generic drug is any less safe or pure than the brand-name drug it mirrors--whether it's an over-the-counter drug or a prescription medication. The FDA regulates generics just as it does brand-name drugs and monitors them once they're on the market. To date, the FDA has found no difference between generic and name-brand drugs in the rate of adverse reactions.

To win FDA approval, a generic-drug maker must prove that its product contains the identical active ingredients as its brand-name counterpart. The manufacturer must also show that the generic is bioequivalent, usually by demonstrating that the active ingredient enters and leaves the bloodstream as rapidly and completely as its branded twin. Generic drugs that do should have the same therapeutic effect.

If you're taking a pricey brand-name drug that is still under patent, you may be able to switch to a generic of another drug in the same therapeutic class that would work just as well--or even better--and cost far less. In that case, however, you would be taking a different drug, so talk to your doctor about possible differences in effectiveness and side effects.

Trademark laws prohibit a generic drug from looking exactly like other drugs on the market. After all, brand-name companies have made distinctive colors, shapes, and sizes part of their sales strategy. (Remember the ads urging consumers to take the "purple pill" for heartburn?) Also, brand-name pills and generic pills often have different inactive ingredients, such as flavorings, that affect taste. Keep in mind, though, that the shape, size, and taste of the pill have no impact on how well it works.

Some doctors write a prescription for a brand-name medicine and leave it to the pharmacist to substitute a generic when applicable. Every state has some type of law allowing pharmacists to do this unless the doctor specifies otherwise. To save yourself any confusion, talk with your doctor about your prescription when he or she is writing it. Ask whether the prescription is for a brand-name or generic drug and why the doctor has prescribed one or the other. It makes sense to let the doctor know that you would prefer the less expensive choice as long as safety and effectiveness are equivalent. For more information about generics, see the Q & A on generic drugs found at the FDA's Center for Drug Evaluation and Research.