As reported at MMAJunkie, Koscheck has suggested Olympic style drug testing for his upcoming match with GSP and GSP is, it appears from the article, amenable to any such testing.
I have previously posted a few times about the USADA testing protocol (largely in response to the Mayweather Mosley fight and Mayweather and Pacquiao negotiations) here.
Once again, in the context of drug testing, fighters are exchanging charges and counter-charges concerning use of banned substances. As I have previously posted, these charges can lead to litigation of defamation claims.
Specifically, there is currently litigation pending in the United States District Court for Nevada involving Pacquiao's claims of defamation against Mayweather, de la Hoya, Richard Schaefer et al. and their alleged statements in connection with Pacquiao's failure to agree to blood testing leading up to the fights during the first round of negotiations with Mayweather. ( I have posted about that litigation here and here).
Given the potentially damaging nature of any charge of another fighter's use of PEDs, fighters should be particularly careful about what they say in this regard. Here are some general (and practical thoughts) on the matter.
First, while truth is a defense to a defamation claim, getting to the "truth" often takes litigation (and discovery) and so merely thinking something is true (without more) does not shield a fighter from liability for making these claims. (That said, a fighter who has used PEDs in the past would likely never bring such a claim in the first instance and risk confirmation of any hypothetical past use).
Similarly, although repeating another's defamatory statement without asserting any direct knowledge concerning the truth of the matter asserted is an interesting tactic, for the most part, courts have found such efforts to repeat defamatory statements (while denying actual knowledge of their truth) to be actionable.
Second, while big-name fighters are limited public figures (it is harder for a public figure to prevail in a defamation action than it is for a non-public individual because the public figure must allege actual malice, which is defined as knowledge that the statement was false or reckless disregard of whether it was false or not), a fighter charged with drug use can certainly allege actual malice and bring an action for defamation. Again, it may be difficult to prevail as a public figure, but that doesn't prevent the aggrieved fighter from commencing litigation and causing the other fighter "pain" in the form of legal fees, lost time for depositions etc.
Finally, although statements of fact can be defamatory whereas statements of opinion generally are not, often times the line between fact and opinion is blurry. And again, nothing prevents the aggrieved fighter from commencing litigation and letting the court sort through the statements to parse those that are fact from those that are opinion.
Bottom line, to be safe, fighters should avoid making accusations of drug use and let the tests themselves do the talking.