From this story in the Washington Post:
When Baltimore Ravens linebacker Ray Lewis tore his triceps last fall and worked his way back onto the field with a remarkably quick recovery, he was given a product that contains a substance banned by the NFL, Sports Illustrated reports. _Lewis, asked about the report during media day, denied using the substance and pointed out that he has never tested positive for banned substances. Mitch Ross, a co-owner of Sports with Alternatives to Steroids said he spoke with Lewis after he was injured Oct. 14 and that Lewis requested products that could speed his recovery time. Among the treatments was deer-antler spray, which contains IGF-1, which is on the list of substances banned by the league.
According to the story, IGF-1 is a natural, anabolic hormone derived from deer antler that stimulates muscle growth, which the NFL views as a performance-enhancing drug. The owner of the company Lewis allegedly received his spray from uses deer from New Zealand to extract the substance.