The football career of Baltimore Ravens linebacker Ray Lewis has been equal parts celebrated and controversial. But the buildup to this Sunday’s Super Bowl—Lewis’ final game—has provided one of the strangest twists yet.

Lewis is alleged to have used deer antler spray in his recovery from a triceps injury earlier this season. The spray in question contains insulin-like growth factor 1 (IGF-1), a protein that occurs naturally in humans and is believed to aid in muscle recovery. While IGF-1 is banned by various competitive athletic leagues (the NFL included), it is widely available in sprays or pills.

Christian Sell, Ph.D., is an associate professor in the Department of Pathology & Laboratory Medicine at Drexel University College of Medicine. Dr. Sell has studied IGF in aging and lifespan extension for the past 10 years.

“Insulin regulates metabolism in the body, while IGF regulates cell growth and survival, as well as body size,” says Dr. Sell. “IGF that is circulating in the blood is made by the liver, and growth hormone drives the expression and production of IGF. Every cell in the body will respond to IGF-1 by growing—it’s basically an anabolic.”

A deer’s antlers grow faster than the body itself—due in large part to the heavy presence of IGF-1. Dr. Sell went on to say that when someone takes growth hormone, what they are hoping to accomplish is the ignition of IGF’s role in the body. That’s why IGF is used in the treatment of children who aren’t growing at the expected rate. One reason IGF-1 is attractive to competitive athletes is that unlike other substances, it cannot be detected in a urine test.

One question is the viability of IGF-1 when used in spray form. Injection is the preferred method when given to children with growth deficiencies, but in the cases of elite athletes, many are believed to have used IGF-1 by spraying it under their tongues, where membranes are more permeable to allow for absorption into the bloodstream. Experts are skeptical whether this method of ingestion could have performance-enhancing effects.

“I won’t rule it out,” says Daniel Hussar, Ph.D., professor of pharmacy at the Philadelphia College of Pharmacy at the University of the Sciences. “But I’ve seen very little information to that effect. I’m reluctant to accept the suggestion that as a spray, this is doing much of anything.”

More likely, he continues, individuals who are using IGF-1 may be using other products—or are already in top physical condition and therefore experience faster healing. But once deer antler spray is introduced to the equation, those factors are ignored and all healing is attributed to the added presence of IGF-1.

“A spray under the tongue?” asks Dr. Sell. “I don’t think that’s going to have an effect. IGF doesn’t just float around in the body—it’s carried by proteins that are critical for regulation. Without those, it’s has a half-life that’s literally a minute or two. So I can’t see it having much of an impact in spray form.”

Regardless, another major sporting event will take place under the specter of performance-enhancing substances. For his part, Ray Lewis denies any usage of the spray, pointing to his squeaky-clean record of never testing positive for a banned substance in his 17-year NFL career. But in today’s sports culture—and perhaps with good reason, given recent happenings in other sports—athletes are often presumed guilty anytime such allegations present themselves.