Over-the-counter pain relievers are widely available and require no prescription. But this doesn't mean they're completely safe, warns the June issue of the Harvard Women's Health Watch. Non-prescription analgesics have side effects, and can interact with other drugs, dietary supplements, and alcohol.

They also have the same active ingredients found in many combination products for colds, flu, and allergies. So if you're taking several medications, you may be getting more of a particular pain-reliever than is safe.

Nonsteroidal anti-inflammatory drugs (NSAIDs) such as aspirin and ibuprofen reduce pain, inflammation, and fever. Older people and those who take high doses for a long time for conditions such as osteoarthritis are at risk for stomach inflammation, peptic ulcers, and intestinal bleeding. Overuse may also cause ringing in the ears, dizziness, kidney and liver problems, and high blood pressure.

Acetaminophen relieves pain and fever by a somewhat different mechanism than NSAIDs, but it, too, can cause serious problems. For example, taking too much can lead to liver damage. Consequently, if you drink regularly or have liver problems, you should steer clear of acetaminophen.

The Harvard Women's Health Watch says the best way to avoid trouble with over-the-counter pain relievers is to become informed about how they work and the potential pitfalls of using them. The article describes the science behind NSAIDs and acetaminophen, flags potential sources of trouble, and tells you what to avoid while taking these drugs.

The Harvard Women's Health Watch is available from Harvard Health Publications, the publishing division of the Harvard Medical School. You can subscribe at www.health.harvard.edu or by calling 1-877-649-9457 toll-free.

Harvard Health Publications publishes five monthly newsletters as well as more than 50 special health reports and books drawing on the expertise of the 8,000 faculty physicians at Harvard Medical School and its affiliated hospitals. For more information visit http://www.health.harvard.edu/women