Former Bath and Australia lock Justin Harrison has been suspended for eight months after admitting three charges, including taking illegal drugs.
The 35-year-old, who abruptly retired at the end of last season, was found guilty of "actions prejudicial to the interests of the game".
Harrison also admitted shouting "class A, it's OK, everyone's doing it" in the vicinity of Bath academy players.
And the former Ulster lock also pleaded guilty to missing a club drugs test.
Harrison's case was heard by a Rugby Football Union disciplinary officer Jeff Blackett on 16 July, with the judgement ruling him out of playing or coaching until 13 January 2010.
But Harrison avoided an automatic two-year ban under World Anti-Doping Agency (Wada) rules because the incident happened out of competition and instead has been punished under RFU charges.
The issue stemmed from an end-of-season party in London on 10 May which began at 1300 BST at The Church before moving on to The Walkabout in Shepherd's Bush, where Harrison was asked whether he would like some "gear".
He said he had never taken cocaine during any rugby season in the past and had been regularly tested throughout his career, but on this occasion had made the decision to take the substance.
I am grateful for the opportunity to remain involved in the game and I fully intend to use my own experiences to educate younger players in the future
Towards the end of the evening, the Bath players clashed with Harlequins players celebrating at the Pitcher and Piano, with both sets of players having consumed significant quantities of alcohol.
An altercation between Harrison and an unnamed Quins player erupted, with the second row knocked to the ground.
In the wake of the incident, Bath's management received allegations that some players, including Harrison, may have been using drugs.
Harrison was contacted by the club on 12 May and asked to undergo a drugs test on 13 and then 14 May.
On the latter date, Harrison met with Bath chief executive officer Bob Calleja and submitted his resignation.
An RFU investigation revealed Harrison had made references to social drugs in a jocular manner when he mimicked a flight attendant in an aircraft with the quote: "class A, it's OK, everybody is doing it" on the bus during the night out in London.
Harrison said there were Bath academy players on board and admitted he had acted inappropriately.
Following his resignation, Harrison acknowledged he had damaged the reputation of the game and withdrew from two Barbarians matches against England and Australia.
Harrison's counsel, Owen Eastwood, said his client "took full responsibility for his actions - which were his alone".
Harrison has also lost his right to work in the UK, damaging his post-playing career prospects should he move into coaching, and would be subjected to regular testing at least four times a year should he continue to play professional rugby.
"I wish to express my acceptance of my suspension by the RFU," read a statement issued by Harrison.
"I deeply regret the incidents of Sunday, May 10, 2009 and the subsequent damage to Bath and the game itself.
"I am grateful for the opportunity to remain involved in the game and I fully intend to use my own experiences to educate younger players in the future."
Harrison's former Bath team-mates Michael Lipman, Alex Crockett and Andrew Higgins have also been charged with conduct prejudicial to the interests of the game.
The trio resigned from the club after allegedly refusing to undergo drug testing.
In February, Bath and England prop Matt Stevens was given a two-year ban after testing positive for cocaine.
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