CHICAGO — Mikey Santini was in junior high when he started taking creatine and protein supplements to build muscle and enhance his athletic abilities. By his junior year at Stevenson High School, he had moved on to nitric oxide "energy igniters" such as N.O.-Xplode and so-called "legal anabolic" products such as Mass FX, which claims to boost strength, aggression and testosterone levels.

Some surveys show anabolic steroid use has decreased among adolescents over the last decade, but a popular alternative for many athletes — over-the-counter supplements — is raising concerns among parents, coaches, the U.S. Food and Drug Administration and even lawmakers.

Proponents say the legal products can provide a competitive edge and fill in nutritional gaps for athletes with hectic schedules and poor diets. But supplements, which are as easy to buy as aspirin, can pose risks to young athletes, whose developing bodies often are undergoing rapid physical changes. The long-term health effects of commonly used products such as creatine aren't known, but children often mix products or take more than the recommended amounts, and most of the safety research has been done on adults.

The FDA, which has limited ability to regulate dietary supplements before they hit the market, recently prompted several major recalls of bodybuilding supplements and warned consumers to avoid products marketed as alternatives to anabolic steroids.

"(Supplements) are actually more of a potential problem in our society than steroids," said C. Roger Rees, a professor of human performance sciences at Adelphi University who specializes in social issues and high school sports. "Kids see supplements as safe and they're sold over the counter. I'd be concerned about large use if I was a parent."

For athletes, the benefits of taking supplements rarely outweigh the risks. With the exception of creatine, there's little evidence that sports supplements, a $2.7 billion industry in the U.S., actually enhance performance. Yet even seemingly benign ingredients have potential dangers.

Protein, for example, is relatively safe. But some products may contain multiple sources of protein, said personal trainer Erin Palinski, a registered dietitian who specializes in adolescent athletes. In general, athletes need 2 grams of protein per kilogram of body weight. "Teen athletes who get too much can excrete calcium, which could decrease bone mass," Palinski said. "Since that's prime time for bone building, it could lead to future problems."

Creatine, which the American College of Sports Medicine says shouldn't be used by those younger than 18, has been shown to be ineffective for some people. It can cause stomach upset and muscle cramps and overwork the kidneys. There are no data evaluating the long-term consequences of use or its effect on the heart and brain.

Comprehensive research on supplement use among high school athletes is scarce. One 2006 study of 139 Nebraska high school athletes found 22 percent took dietary supplements. Other research shows use ranging from 8 percent to 58 percent among high school athletes. And though many high school coaches encourage exercising and eating well and don't promote any products beyond generic protein shakes, some acknowledge that teens aren't open about what they do off the field.

"It really picks up in the offseason," said Santini. "I know people who have no idea what's going into their body but they've put on 20 pounds in two or three weeks." The FDA, concerned about the escalating use among minors, has started taking a closer look at products on store shelves. Last month, the federal agency triggered recalls of more than 70 dietary supplements that may contain ingredients—such as "Superdrol," "Madol," "Tren," "Androstenedione" and "Turinabol"—that are classified as steroids. In June the FDA issued a public health alert warning consumers about bodybuilding supplements that claim to boost or diminish the effects of hormones because they could contain undeclared steroids, in part to protect unwitting high school athletes, said attorney Mike Levy, the director of the FDA's office of compliance in the division of drug evaluation and research.

Congress, meanwhile, is investigating whether regulations for bodybuilding dietary supplements need to be strengthened. Unlike food and drug products, the 10,000 supplements on the market are not approved by the FDA for safety and efficacy before they hit the market. Instead, under the Dietary Health and Supplement Education Act of 1994, it's up to the manufacturer to make sure the product is safe. The FDA can take action only after the products are on store shelves.

Others say supplements such as protein and creatine, which can both be found naturally in whole foods, can be beneficial for teen athletes whose busy schedules and notoriously poor diets make it hard to get proper nutrition. Ingesting small amounts of protein and carbohydrates before and after exercise has been shown to have positive effects.

"I'm often ridiculed by my colleges for my unwavering belief in supplementation and its ability to positively affect athletic performance," Banda wrote in his e-book, "Nutritional Supplements for Sports and Wellness." "But in an increasingly competitive world, optimal supplementation can mean the difference between coming in first place or bringing up the rear."

Brian Grasso, who specializes in youth athletic development, has no problem with certain supplements such as protein or fish oil — as long as athletes have sound nutritional habits. He worries, however, that creatine can be a gateway drug. "Once you start dabbling in ergonomic (performance enhancing) aids, my concern is they become addictive and are not enough," said Grasso, founder and CEO of the International Youth and Conditioning Association. "It opens the door to steroids."

Santini, who now is studying criminal justice at the College of Lake County, Ill., gleaned his information on supplements from the Internet and friends. He works out two to three hours a day and boosts his effort by taking Mass FX, Mass Caps, naNO Vapor, protein powder, creatine, milk thistle and 60 to 80 fluid ounces of water. Some of the products he was using have been recalled by the FDA, but he said he can still get them on the Internet and plans to stock up.

"I like the feeling of being in shape, maximizing my athletic abilities and making the most out of my strength and potential," he said.