Watson insists he has done nothing wrong, having followed advice from Essendon medical staff, and he was surprised by WADA's statement last month confirming the drug was banned.
But WADA president John Fahey said on Tuesday "nothing has changed" and repeated the obligations athletes are under.
"You are responsible for what goes into your system, it's a strict liability," Fahey told AFL.com.au.
"Now whether or not there's any mitigating circumstances depends on individual cases, and that's a matter for ASADA who are currently investigating it.
Fahey wouldn't comment specifically on Watson's revealing interview on Fox Footy's On The Couch program on Monday night.
"I won't comment on that, that's a matter for ASADA ... any comments I make would only complicate that," he said.
Fahey said he had no issue with the time the Australian Sports Anti-Doping Authority was taking to investigate the allegations against Essendon.
"Lance Armstrong, start to finish, took somewhere like two and three-quarter years. These things take what they take, it's as simple as that," Fahey said.
The WADA boss said his organisation would review the Bombers' case only once the ASADA and AFL process had finished.
"We look at the results when it's concluded, we look to see if the code is being applied correctly, if it hasn't been applied correctly we have the right of appeal," Fahey said.
He said WADA could lodge an appeal on behalf of either his organisation or an accused athlete if it believed they had been treated unfairly.
"We can appeal on behalf of either if we don't believe the code has been applied in a correct manner," he said.
It is unlikely the League will make any comment about Watson's revelations on Tuesday.
Matt Thompson is a reporter for AFL Media. Follow him on Twitter @MattThompsonAFL