Zach Jafarzedeh claims Bobbi - who is fighting for her life in hospital after being found face down in her bathtub on 31 January - used to take the anti-anxiety drug, which helps prevent panic attacks, on a regular basis and believes she may have done so following a disagreement with Nick Gordon.
The 21 year old - who stayed close to the 21-year-old aspiring actress, claims Bobbi has been taking Xanax since she was 16, after dating her in their teens, he said: "I know they got into a fight a few days before and she was really depressed about that and probably took a few Xanax and bathed and fell asleep.
"She would take more than she was prescribed of the Xanax.
"If you take two or three of them, you will black out and not remember anything.
"No matter who you are, it's going to knock you out, and mixed with alcohol it's a deadly combo."
Zach also admitted Bobbi, who is in a medically-induced coma in an Atlanta hospital, may have tried to commit suicide in the bath because her late mother Whitney Houston - who accidentally drowned in a bathtub in a Beverly Hills hotel in February 2012 - passed away in similar circumstances.
He explained: "Some of it makes me feel like it could be a possible suicide, not even just a mistake. Something symbolic like, 'This is the way my mom died, this is the way I want to kill myself too.'
"It's eerie how similar that is. It sent chills down my spine and it made me sick to my stomach when I heard about it."
Despite claiming Bobbi and Nick - who her father Bobby Brown has insisted she is not married to, despite the pair's previous claims - fell out days before she was found in the bath, Zach doesn't believe he would beat her up and put her in the tub.
He added to Daily Mail Online: "Everybody's trying to make it all, 'Nick Gordon beat her up', but I don't believe that.
"I don't believe he beat her up and threw her in the bathtub. That's kind of stupid, why would you put her in a bath if her mom just died in a bathtub?"
This comes after it was reported that Nick is no longer welcome in Bobbi's family home.
An insider said: "Nick has been told the townhouse is no longer available for him to live in and to find other living accommodation."
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