Charles Hennekens of Harvard Medical School led one of the studies. In 1983, he began to study more than 22,000 healthy male doctors over 40 years of age. Half took an aspirin every other day. The others took what they thought was aspirin. But it was only a placebo, an inactive substance. Five years later, Dr. Hennekens reported that people who took aspirin reduced their risk of a heart attack. But they had a higher risk of bleeding in the brain than the other doctors.

A few years ago, a group of experts examined studies of aspirin at the request of federal health officials in the United States. The experts said people with an increased risk of a heart attack should take a low-strength aspirin every day. Aspirin may help someone who is having a heart attack caused by a blockage in a blood vessel. Aspirin thins the blood, so the blood may be able to flow past the blockage. But experts say people should seek emergency help immediately. And they say an aspirin is no substitute for treatment, only a temporary help.

But what about reducing pain? Aspirin competes with other medicines for reducing pain and high body temperature. The competition includes acetaminophen, the active substance in products like Tylenol. It also includes ibuprofen, the active substance in products such as Advil. Like ibuprofen, aspirin is an NSAID -- a non-steroidal anti-inflammatory drug.

Several studies have found that men who take aspirin or other NSAIDS have a decreased risk of prostate cancer. The prostate is a gland and part of the male reproductive system. Researchers at the Mayo Clinic in Minnesota wanted to see how NSAIDs might affect prostates that are enlarged, but not cancerous. They followed the health of 2,500 men for 12 years. The researchers said these drugs may delay or stop development of an enlarged prostate. They said the risk of an enlarged prostate was 50 percent lower in the NSAID users than the other men. The risk of bladder problems was 35 percent lower.