ESSENDON have reportedly admitted to drug investigators some of their players took the anti-obesity drug AOD-9604 last year.
The Bombers said they relied on a document purported to have been issued by the World Anti-Doping Agency approving use of the substance, which WADA confirmed this week was banned.
It is alleged Essendon's former sports scientist Stephen Dank showed a document to Bombers club doctor Bruce Reid.
Essendon does not have the letter, and believe Dank has the only copy.
Several Essendon officials are aware of the letter's existence.
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