CHICAGO -- As part of her marathon training, Daisy Carranza has taken an over-the-counter pain reliever nearly every day for the last several months.

On race day, she's prepared to pop at least seven Extra Strength Tylenol capsules: two at the starting line, three at mile 18 -- just before the body starts to rebel -- and two at the post-race party, to help with recovery.

"It's a regular thing," said Carranza, 31, of Chicago, who is entered in her fourth Bank of America Chicago Marathon. "I have a lot of knee, back and shoulder pain, so I look at Tylenol in the same way as protein bars and Gatorade."

Like lucky caps and favorite shoes, marathoners often rely on over-the-counter pain relievers to get them through both the endless training and the grueling 26.2-mile race itself. The most popular drugs generally contain acetaminophen -- the active ingredient in Carranza's Tylenol -- or ibuprofen, part of a class of medications called NSAIDs, or non-steroidal anti-inflammatory drugs.

The medications can be a godsend when taken as directed: for headaches, fevers or acute injuries, such as a twisted ankle. But both ibuprofen and acetaminophen pose well-documented health risks, especially when they're consumed in large amounts or for an extended time.

There's also little evidence to suggest that athletes receive any benefit from taking pain relievers before a race. And emerging research is starting to show that ibuprofen can actually cause inflammation under certain conditions and may interfere with the body's processes of recovery and adaptation.

"We fall into the assumption that anything available over the counter is safe and that we know how to use it," said Wendy Kohrt, a professor of medicine at the University of Colorado Anschutz Medical Campus who has studied NSAIDs' effects on bone formation. "But it's just not true."

When taken preventively, pain relievers "have the potential to reduce how well your tissues adapt to the exercise," said Stuart Warden, an associate professor in the Indiana University School of Health and Rehabilitation. "We all know exercise makes muscles bigger, bones stronger and tissues adapt, changing in structure," he said. "NSAIDs block a pathway that's important for that adaptation."

Athletes in all sports and at all levels swear by over-the-counter painkillers, especially ibuprofen, which is known by its fans as "Vitamin I." A 2008 survey of participants in an Ironman triathlon in Brazil found that almost 60 percent reported using NSAIDs in the three months leading up to the event, according to a study in the British Journal of Sports Medicine. Almost half reported taking pills during the race.

Another report that looked at medication use by male soccer players competing in the 2002 and 2006 World Cups called the high intake of NSAIDs "alarming."

Athletes often take pain relievers to help cope with pain after intense exercise, including a condition called delayed-onset muscle soreness. But NSAIDs haven't been shown to help with that problem, Warden said. Instead, runners should try gentle exercise, such as using a stationary bike or running in water, he said. Sprinting and normal running should be avoided.

Ibuprofen (Advil and Motrin) and another NSAID, naproxen (Aleve), are recommended for pain relief and reducing fever. Best tolerated when taken on a full stomach -- rare during a marathon -- they work by stopping the body's production of a substance that causes pain, fever and inflammation.

But that substance, prostaglandin, is also important for the synthesis of collagen, Warden said. "Collagen is the main structural material of all muscles, bones and tendons," he said. "That's what gives [them] strength. The drugs can reduce how much collagen you form in response to exercise."

Acetaminophen has a weaker anti-inflammatory effect than the NSAIDs and is often classified as an analgesic, or pain reliever. The drug changes the way the body senses pain and has a cooling effect, according to the National Institutes of Health.

Both types of medicines have risks and potential side effects, especially when misused. (Experts are less concerned about aspirin, also an NSAID, but say it's best to avoid routinely taking any kind of painkiller before running.)

With the exception of aspirin, NSAIDs can increase the risk of heart attack and stroke, and taking them while dehydrated can cause gastrointestinal pains and overwhelm the kidneys.

"There's absolutely a role for anti-inflammatories like Motrin, Advil and Aleve, but you have to understand when they're necessary and when you should take them, said Dr. George Chiampas, medical director for the Chicago Marathon. "And more is definitely not better."

Taking too much acetaminophen -- a common mistake because it's often found in combination products -- can cause liver damage. Last year, Tylenol's manufacturer lowered the recommended daily maximum dose of Extra Strength Tylenol from eight 500 mg tablets to six to reduce the risk of an accidental overdose.

Soreness is one of the least welcome side effects of exercise, but the pain is a signal that some tissue irritation or damage has occurred, said Warden. Masking that pain can lead to a more serious injury.

By the same token, inflammation is a natural part of the healing process and speeds up tissue repair. A chemical release at the injured site attracts cells that will clean up the area and heal it, said Warden.

The inflammation response often is overzealous, Warden said, and drugs can be used to control it. "But once the inflammatory signs are gone, you don't need anti-inflammatories," he said.