From this story on SI.com:
_Baseball sent a warning to its major and minor league players last week that may sound odd, if not comical, but is a sign of these drug-testing times: stop ingesting deer antler spray. Until the warning went out, baseball players, taking their cues from the body-building and NFL cultures, felt safe using a deer antler spray as an alternative to steroids with almost no risk of flunking a drug test. Deer antlers? Yes, chemists have figured out that the velvet from immature deer antlers includes insulin-like growth factor, or IGF-1, which mediates the level of human growth hormone in the body, and is also banned by MLB and the World Anti-Doping Agency, among others, for its muscle-building and fat-cutting effects.