The 20-year old striker was filmed inhaling the 'laughing gas' from a balloon while sitting in his car after Albion's 3-0 loss to Manchester United on March 8.
England U21 international Berahino slumped over his steering wheel after taking in the legal but potentially harmful substance and has since been reprimanded by the Baggies for his bizarre conduct.
"I have spoken to Saido about the incident and told him in no uncertain terms that his conduct is not befitting a West Bromwich Albion player," said West Brom's sporting and technical director Richard Garlick.
"Saido knows he has made a mistake. He has apologised for his actions and has assured the club it will not happen again."
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