The Australian Sports Anti-Doping Authority has warned that the banned drug two Collingwood footballers have tested positive for can prompt a stroke.
Magpies Lachie Keeffe and Josh Thomas have returned positive tests to clenbuterol.
In a statement, ASADA said "Clenbuterol is classed as an S1 anabolic agent on WADA's prohibited list and is prohibited in and out of competition.
"Unsupervised use of clenbuterol can worsen pre-existing heart conditions or hypertension, and there is a risk of overdose and stroke when used at high doses. It is a potentially dangerous drug that, as well as being banned under the prohibited list, is not approved for human use in Australia."
ASADA said "out-of-competition samples were collected by ASADA from two players on 10 February 2015. 'A' samples from both players returned a positive result for the prohibited substance clenbuterol."
The Magpies had just returned from their pre-season camp in New Zealand when the players were tested.
"On 6 March 2015, after receiving advice from a WADA-accredited laboratory in relation to both players' samples, ASADA commenced an investigation. ASADA is unable to elaborate on the investigation process as it remains ongoing," the agency said.
"At the appropriate time in ASADA's investigation and after concluding its legislative processes, ASADA notified the two players on 27 March 2015 of the 'A' sample test results."
