More than one-third of sport supplements available online in Australia contained substances banned by the World Anti-Doping Agency (Wada), according to a survey commissioned by the national doping watchdog.
The survey tested 200 products including amino acids, protein powders and others marketed as "muscle builders" and "fat burners", Sport Integrity Australia (SIA) said.
The tests, run by Human and Supplements testing Australia, found 35 per cent of the products contained substances listed on Wada's banned list.
"Athletes need to understand that using supplements always carries risk," SIA Chief Science Officer Dr Naomi Speers said in a statement on Wednesday.
"Products marketed for fat burning, muscle building or pre-workout are particularly risky."
The survey found 57 per cent of the products that had Wada-banned substances did not list them on labels on their packaging or websites.
Five of the products lacked any unique identification on their labels, making them non-compliant with local laws for food and therapeutic labelling.
Sports supplements containing banned substances triggered Australia's biggest case of mass doping in professional sport.
Thirty-four Australian Rules footballers at the Melbourne-based Essendon Bombers club were found guilty in 2016 of taking banned substances during a club-led supplements programme, with most players given two-year suspensions.