With regard to drug testing, whether or not a requirement to disclose prescription medications exists depends entirely on why the individual is testing. I'm the court liaison for a large agency that deals primarily with urinalysis drug testing, and whether or not people must, or even are able to, disclose to us what they're taking on a prescription basis varies from program to program.

People testing for the Diversion or Deferred Prosecution program have to tell us what they're taking if they want to participate in the program; they are free to refuse, at which point they're terminated from the program and go back to court to face the music. Probation clients report their prescription drug use to their POs - we don't really care; the same for folks testing for CPS - their case workers require that information, but the testing agency does not. People testing for Family Court don't have to tell anyone, but if they test positive for something, it's a sure bet that the court and attorneys are going to be asking why.

I have no idea how the matter of prescription drug use is handled in the MLB testing program, but I suspect that it's done like with most private employers: if you test positive for what may be a controlled substance, you can either prove that you were legally entitled to use that substance, or you will be presumed guilty. In other words, you may not be legally required to provide information about your medical condition or what you're taking for it...but if you want to keep your job, you probably should.

In any case, the lab cannot, and does not, assume or report that you - for example - tested positive for steroids because you're taking a scrip that has steroids in it; someone could be taking a herpes medication that contains steroids and taking steroids as a PED. That's a big part of the reason that athletes are prohibited from taking some medications that they'd otherwise be legally entitled to take - the test only tells you so much, and there is no test for "intent".