The World-Anti Doping Agency (Wada) has discovered a second "designer steroid" in the wake of the ongoing THG scandal, BBC Sport has learned.
A sample of the new steroid has been seized by Canadian customs officers at the border with the USA.
Wada says the drug has been developed specifically for use by athletes.
"This is the second designer steroid we have found," said Wada's Olivier Rabin on Tuesday. "We believe this was created purely for doping in sport."
The new steroid was created in a laboratory and would have a similar impact to testosterone if used, increasing strength, muscle bulk and stamina.
Several leading track athletes, including double world sprint champion Kelli White and Britain's European 100m champion Dwain Chambers, have been banned after THG (tetrahyrogestrinone) was discovered in 2003.
Rabin, Wada's scientific director, said a desoxy-methyl-testosterone (DMT) had been discovered after an anonymous tip-off and a test had been developed.
"This proves that THG was not a one-off," he said.
"This new substance has been discovered so quickly after THG because we learned some lessons from the THG story.
Rabin said the discovery of the new steroid had put Wada "ahead of the dopers", adding: "This shows them how serious we are."