Nigella Lawson has admitted in court she used cocaine "several times", but insisted she is not a habitual user of the drug.
The 53-year-old said she had used the drug half a dozen times when her then husband John Diamond was terminally ill and in 2010 when she was subjected to "intimate terrorism".
She also admitted smoking cannabis in the last year of her marriage to Charles Saatchi, but said she has now given up.
She said: "I have never been a drug addict. I've never been a habitual user. There are two times in my life when I have used cocaine.
"I have to be honest, I have smoked the odd joint. It's a false friend and not a good idea.
"I have to say, since freeing myself from a brilliant but brutal man, I'm now totally cannabis, cocaine, any drug-free."
Francesca, left, and Elisabetta Grillo deny the fraud charge
Ms Lawson said the first instance was with her late husband when he found out his cancer was terminal, and said she had taken it with him on six occasions. The second occasion was when a friend gave the drug to her.
She added: "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 claims she was a drug addict were "absolutely ridiculous".
Ms Lawson was giving evidence at Isleworth Crown Court at the trial of two former personal assistants accused of spending thousands of pounds on company credit cards.
Earlier on Wednesday she claimed allegations of drug abuse had been spread by her ex-husband Charles Saatchi in an attempt to ruin her reputation. She also claimed it was a "witch hunt".
She said: "I have been put on trial here where I am called to answer, and glad to answer the allegations, and the world's press, and it comes after a long summer of bullying and abuse.
"He (Saatchi) had said to me if I didn't get back to him and clear his name he would destroy me."
Following a much-publicised incident at Scott's restaurant in Mayfair, London, where her ex-husband was pictured with his hand on her throat, false allegations of drug abuse about her began circulating on a "PR blog" she said.
She said these allegations were "dedicated to salvaging Mr Saatchi's reputation and destroying mine".
Ms Lawson claimed in court the incident was sparked when she commented on a person walking by with a baby.
Mr Saatchi was pictured with his hand on Nigella's throat in June
She said: "I said 'I'm so looking forward to having grandchildren'.
"He grabbed me by the throat and said 'I'm the only person you should be concerned with'."
It is alleged that between January 1, 2008, and December 31, 2012, Italian sisters Elisabetta and Francesca Grillo committed fraud by abusing their positions while working for the couple.
The jury was told they are accused of using credit cards loaned to them by the TV chef and art dealer to spend more than £685,000 on themselves.
Prosecutors claim the women lived the "high life", spending the money on designer clothes and handbags from Louis Vuitton, Christian Dior and Vivienne Westwood.
Ms Lawson told the court: "It's very difficult when you find out that someone you have loved and trusted could behave that way.
"In my heart of hearts I do not believe Lisa (Elisabetta) to be a bad person. I believe her not to have a very strong moral compass.
"She broke our heart."
She added that she once took out £7,000 from her savings to pay for Elisabetta Grillo to have her teeth fixed.
Elisabetta, 41, sometimes referred to in court as Lisa, and co-defendant Francesca, 35, both of Kensington Gardens Square, Bayswater, west London, deny the charge against them.
:: Watch coverage on Sky News