"You can get fabulous results," said Santini, 19, of Buffalo Grove, Illinois, who played soccer and ran cross country. But he acknowledges the products have a potentially dangerous downside.
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 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.
Moreover, some see supplements as a bad habit, one that can lead to more dangerous drugs and discourage teens from what they really need: nutritious whole foods. But supplement use is generally overlooked because parents and coaches often have no clue what - or how much - children are actually taking.
"(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.
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.
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.
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.
Supplements marketed as prohormones or testosterone-boosters such as DHEA (dehydroepiandrosterone), meanwhile, have been linked to prostate cancer; side effects include male breast development, heart problems and hormonal changes in both men and women.
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.
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.
But sports supplement attorney Michael DiMaggio, of New York, said the majority of manufacturers produce safe products. Moreover, most are labeled for those older than 18 and often 21.
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.
Athletes say the pressure to succeed and the desire to keep up with peers often drives supplement use. Though whey or soy-based protein supplements are among the most popular products, creatine is frequently used by boys participating in team power sports such as football, wresting and hockey.
Perhaps the biggest problem is that the supplement world is shrouded in mystery, said Pieter Cohen, an internist at Cambridge Health Alliance in Massachusetts and an instructor at Harvard Medical School. The FDA doesn't know about potential side effects because premarket testing isn't required, there aren't any studies on whether they have positive or negative impacts on teenagers and adolescents are unlikely to tell doctors what they're taking, Cohen said.
Santini, who now is studying criminal justice at the College of Lake County, 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.
"I like the feeling of being in shape, maximizing my athletic abilities and making the most out of my strength and potential," he said.