Cardiff Met RFC player Oliver Bilton has been banned from all sport for two years after failing a drugs test.
Bilton tested positive for Oxandrolone and metabolite Epioxandrolone, an anabolic steroid, following an in-competition test by UK Anti-Doping (UKAD).
The forward was tested after a Swalec Championship match between Cardiff Met and Narberth on 13 December 2014.
He is banned from all competition until 12 December 2016.
Bilton, a student of Sport and Exercise Science at Cardiff Metropolitan University, claimed to have ingested the prohibited substances through his use of sports supplements.
"Oliver Bilton's case highlights that supplements that have not been batch tested are a huge risk to an athlete's future as [they have] jeopardised his playing career and potentially his working career in sport as well," UKAD's chief executive Nicole Sapstead said.
Supplements made headlines after Welsh athletes Rhys Williams and Gareth Warburton missed the 2014 Commonwealth Games for failing drugs tests.
UKAD subsequently found Williams and Warburton had inadvertently taken a contaminated food supplement. Williams, 30, was banned for four months and Warburton, 31, for six. Both have now served their bans and returned to competition.
Meanwhile, the WRU launched a nationwide anti-doping campaign in December, and Wales captain Sam Warburton appeared in a video warning about the consequences of doping.
"Players are encouraged to check the prohibited lists, found via the WRU website which include over-the-shelf medication and supplements," the WRU has said.
Rob Cummings, dean of students at Cardiff Metropolitan University, said: "As this has just come to light, it would be inappropriate for us to comment until we have the opportunity to investigate the situation.
"The University has a disciplinary procedure which is used in such cases, and specifically covers the misuse of drugs. This can lead to a range of sanctions being applied including permanent exclusion."