(MONEY Magazine) – AS RECENTLY AS THE 1950S, MOST PEOPLE had just two choices when they wanted headache relief: They could take an aspirin, or they could take two aspirin. Today, however, the shelves of drugstores practically sag under 179 name brands and innumerable store brands of aspirin and other pain relievers. And no wonder: Business is throbbing. Sales of pain relievers are up 21% in the 1990s, from $2.4 billion in 1989 to $2.9 billion today, according to Kline & Co., a pharmaceutical consultant in Fairfield, N.J.

Despite the best efforts of the pillmakers and their ad agencies to convince you otherwise, there are really only five basic kinds of over-the-counter painkillers: aspirin, acetaminophen, ibuprofen, naproxen sodium and ketoprofen. The table below describes their differences and lists some common brands. Except for acetaminophen, all of the remedies are classified as "non-steroidal anti-inflammatory drugs" (NSAIDs), which relieve pain, fever and inflammation. Acetaminophen works on pain and fever but not on inflammation.

While any of these drugs can handle the most common kind of headache--the "tension" type--no pill is perfect for everybody. Children under age 16 should not take aspirin without consulting a doctor, because of the risk of Reye's syndrome, a potentially fatal disease. People may risk kidney problems if they overuse any kind of NSAID. Overuse can also perpetuate and worsen headaches, says Dr. Alan Rapoport, director of the New England Center for Headache in Stamford, Conn.

People who drink may want to avoid acetaminophen because its interaction with alcohol can cause liver damage, warns Dr. David Flockhart, assistant professor of medicine and clinical pharmacology at Georgetown University Medical Center in Washington, D.C. And if you're anticipating surgery, be sure to tell your doctor if you have been taking aspirin or any painkiller regularly, to avoid bleeding complications.

Finally, if all the news about aspirin's other medicinal powers have tempted you to self-prescribe it, check with a doctor first. Aspirin has been shown to help prevent second heart attacks, and some studies say it may stave off certain kinds of cancer, such as cancer of the esophagus. But it can aggravate other problems, including strokes caused by a ruptured blood vessel. --Susan Berger