She said she hadn’t touched drugs since “freeing” herself from the “brilliant but brutal” Mr Saatchi.
The 53-year-old, who also admitted to smoking cannabis, said the idea that she is a “drug addict or habitual user of cocaine is absolutely ridiculous”.
She was testifying at the trial of Italian sisters Francesca and Elisabetta Grillo, who are accused of committing fraud by abusing their positions by using a company credit card for personal gain.
Earlier in the trial, the court heard of an email Mr Saatchi sent to Ms Lawson, addressing her as “Higella” and claiming she was so out of her head on drugs that she allowed their assistants to spend whatever they liked.
Yesterday, the celebrity cook revealed she took the drug with her late husband, John Diamond, when he found out he had terminal cancer, and again in Jul 2010 during her troubled marriage to Mr Saatchi.
Ms Lawson was giving evidence in the fraud trial of two 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. “It gave him some escape.
“There was another time I took cocaine. In July 2010 I was having a very, very difficult time. I felt subjected to intimate terrorism by Mr Saatchi.”
She said she felt “isolated and in fear of ... just unhappy”.
“A friend of mine offered me some cocaine. I took it.”
She said the experience “completely spooked” her.
“The idea that I am a drug addict or habitual user of cocaine is absolutely ridiculous.”
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.
“I said ‘I’m so looking forward to having grandchildren’,” Ms Lawson told the court. “He grabbed me by the throat and said ‘I’m the only person you should be concerned with’.”
Ms Lawson said she began taking cannabis in the last year of her marriage to the multimillionaire art gallery owner. “I have to be honest, I have smoked the odd joint. I found it made an intolerable situation tolerable.
“It’s a false friend and not a good idea. I found the answer was in changing the situation and trying to create a tolerable situation for me and my family.
“I have to say since freeing myself from a brilliant but brutal man, I’m totally cannabis, cocaine, and drug free.”
Ms Lawson claimed she did not know how to roll a joint, but had asked others in her house to do so.
“This was not behaviour I’m proud of,” she said.
Ms Lawson said she was not a “habitual drug user and drug addict, or a snorter of cocaine for 10 years”.
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.”
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.”
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 this morning to complete her evidence.