Nigella Lawson admitted in court that she had taken cocaine in the past but said the idea that she is a "drug addict or habitual user of cocaine is absolutely ridiculous".
The celebrity cook revealed she took the class A drug with her late husband John Diamond when he found out he had terminal cancer, and on another occasion in July 2010 during her troubled marriage to Mr Saatchi.
Nina Nannar reports:
The 53-year-old, who also admitted to smoking cannabis, was giving evidence in the fraud trial of two of former personal assistants, who are accused of spending hundreds of thousands of pounds on credit cards loaned to them by the food writer and Mr Saatchi.
Standing in the witness box at Isleworth Crown Court in west London, Ms Lawson admitted taking cocaine on six occasions with her late husband Mr Diamond.
Ms Lawson said she felt "isolated and in fear of...just unhappy". She said: "A friend of mine offered me some cocaine. I took it."
Ms Lawson told the court the experience "completely spooked" her.
"The idea that I am a drug addict or habitual user of cocaine is absolutely ridiculous," she added.
Ms Lawson said Mr Saatchi "told everyone" he was taking cocaine out of her nose after he was photographed holding her neck at Scott's restaurant in central London.
She claimed the incident was actually sparked when she commented on a person walking by with a baby.
Ms Lawson said she began taking cannabis in the last year of her marriage to the multi-millionaire art gallery owner.
Ms Lawson claimed she did not know how to roll a cannabis joint but had instead asked others in her house to do so.
"This was not behaviour I'm proud of," she said.
Asked by Anthony Metzer QC, representing one of the defendants, where these drug claims may have come from, Ms Lawson replied: "I believe some of it came from your clients and Mr Saatchi. Not the three most reliable witnesses."
Ms Lawson said she believed Mr Saatchi intended to damage her interests, before adding: "And look how it's played out."
She admitted she had hidden any drug use from Mr Saatchi.
"I could have weathered a conversation about it. I just wouldn't have wanted to," Ms Lawson said.
Mr Metzer asked Ms Lawson if Mr Saatchi had a temper.
"Yes, he did have a temper and I don't think that anyone can be in any doubt he had a temper," she replied.
Italian sisters Francesca Grillo and her sister Elisabetta, sometimes referred to as Lisa, are accused of committing fraud by abusing their positions by using a company credit card for personal gain.
Prosecutors claim the Grillos lived the "high life", spending the money on designer clothes and handbags from Louis Vuitton, Christian Dior and Vivienne Westwood.
The pair are accused of using credit cards loaned to them by the TV cook and her ex-husband Mr Saatchi to spend more than £685,000 on themselves between 2008 and 2012, the jury has heard.
Ms Lawson was told by Judge Robin Johnson she must return to the court in the morning to complete her evidence.
The trial was adjourned until tomorrow.