Former Premiership winner Chris Mayor has been banned from all sport for four years for attempting to use and traffic a banned human growth hormone.
Police found private Facebook messages sent by Mayor about the substance in 2018 on the recipient's mobile phone.
Mayor told a UK Anti-Doping (Ukad) investigation that he had been trying to ease his father's knee pain.
Mayor, 40, and his father were cross-examined in a case brought against him by the Rugby Football Union (RFU).
Officers provided evidence to Ukad in September 2019 that Mayor had asked about the substance containing the drug Humatrope.
The RFU also charged Mayor with possession, but that was not proved.
The former Sale, Northampton and Wasps centre's ban has been backdated to December 2021 and will run until December 2025,
Mayor, who scored a try for Sale when they won the Premiership by beating Leicester at Twickenham in 2006, said he had acted "during a difficult period in his life" and described the messages as a "speculative request".
The RFU said Mayor had specifically named the substance - 72iu Lilly Pens - and argued that there was evidence of the former Southport RFC coach "indicating that he intended to sell pens to others" as part of "substantial steps" to plan trafficking.
In his defence, Mayor said his father was suffering from severe knee pain and needed a knee replacement operation.
Mayor told a hearing: "All I knew was that this person had a substance which was a growth hormone and there was a chance it could help my father with some pain relief."
Mayor's father told examiners that he had not been booked to have a knee operation at the time of the initial message and said he would have been "surprised and alarmed" if his son had given him the growth hormone because it is banned by rugby authorities.
Nick Wojek, head of science and medicine at Ukad, said that Humatrope is a prescription-only Class C drug in the UK which can help athletes speed up recovery from training or injury.
The RFU argued that Mayor's evidence showed he had "effectively accepted" that he was guilty of attempted trafficking of the substance to his father.
Stephen Watkins, the RFU's anti-doping and illicit drugs programme manager, said: "Mr Mayor was a respected professional player and well aware of his responsibilities.
"All rugby players, irrespective of level, are subject to the anti-doping rules which are in place to protect players and the integrity of our sport."
In a pre-prepared initial statement given to Ukad in July 2021, Mayor said he was "devastated, embarrassed and remorseful" for the position he found himself in.