"It may have nothing to do with trainers and electrolytes, " Howman told BBC Radio Five Live.

BBC: SPORT | Tennis | Tennis drug tests questioned

Howman says the list of banned substances runs to 10-15 pages, with hundreds of drugs currently prohibited.

CNN: Hi-tech tests to catch Olympics drug cheats at London 2012

"He's got to follow a certain course, " David Howman, director general of World Anti-Doping Agency, told the AP.

NPR: Lance Armstrong May Not Be Done Confessing

However, Howman said Wada was now undertaking its own investigation, which he hoped would be concluded in a matter of weeks.

BBC: SPORT | Tennis | Tennis drug tests questioned

World Anti-Doping Agency (WADA) director general David Howman told CNN the list of banned substances runs to 10-15 pages, with hundreds of drugs currently prohibited.

CNN: Q & A: Catching dope cheats at the London 2012 Olympics

David Howman, director general of the WADA, which oversees drug testing in the Olympics and other elite-level sports, said the tests have improved and are now a "robust" antidoping measure.

WSJ: Antidoping Officials Pursued Armstrong for Years

The New York Times, citing unnamed associates and anti-doping officials, said Armstrong has been in discussions with USADA officials and hopes to meet with David Howman, chief of the World Anti-Doping Agency.

CNN: Oprah interview with Lance Armstrong airs January 17

"I don't think Ben Johnson would even get to London nowadays -- I think he would be picked up in advance, and many athletes now who think they can get there will be swept away by pre-Games testing, " Howman said.

CNN: Hi-tech tests to catch Olympics drug cheats at London 2012

"Only when Mr. Armstrong makes a full confession under oath -- and tells the anti-doping authorities all he knows about doping activities -- can any legal and proper process for him to seek any reopening or reconsideration of his lifetime ban commence, " Howman, the agency's director general, said Tuesday.

CNN: January 15, 2013 -- Updated 2128 GMT (0528 HKT)