The TV chef was speaking during her second day in court at the trial of her two former personal assistants.
Elisabetta and Francesca Grillo are accused of spending more than £685,000 on credit cards loaned to them by Nigella and her ex-husband Charles Saatchi.
Explaining her admission, Nigella said she would rather be ‘honest and ashamed’ than ‘bullied with lies’.
She continued: ‘I'm not proud of the fact I have taken drugs but that does not make me a drug addict or a habitual drug user.
‘I would rather be honest if ashamed and explain the drug usage ... but I wanted to make sure that I was not being bullied with lies.’
‘Mr Saatchi was not examining me for cocaine. That was a story he made up afterwards to clear his name,’
Nigella also said that stories that Charles was checking her nose for cocaine when he was photographed with his hand on her throat outside Scott's restaurant in London, were ‘peddled’ by her ex husband.
‘Mr Saatchi was not examining me for cocaine. That was a story he made up afterwards to clear his name,’ she said.
She denied lying to police when she disputed the drug allegations against her and said it was the ‘extent’ of her drug use that was untrue.
‘It was not true in that my ex-husband was saying that he was getting cocaine out of my nose at Scott's and that I had been completely off my head for 10 years,’ she said.
She added: ‘If you think I would sabotage my health and leave my children orphans you are wrong.’
When asked about her ex-husband’s domestic role, Nigella revealed that the art-dealer had such careful attention to detail he would order small marks to be removed from walls.
'He is a person with a tremendous eye for detail,’ she said.
Miss Lawson said that among other duties, Francesca would organise Mr Saatchi's frappuccinos and sew buttons on his suits.
'Francesca cleaned the house and she organised his frappuccinos - she would get cold coffees for him,' she added.
'She did whatever he said - if he asked her to go out and buy something, she went out and bought something'.
Nigella was asked about an instance when Francesca was called while on holiday.
The barrister said: 'There was one occasion when you couldn't find the remote, you contacted her in Spain.'
Miss Lawson replied: 'Yes, that would have made Mr Saatchi very irritable.'
Ms Arden asked if Francesca did the food shopping, to which Miss Lawson replied: 'I do a fair amount myself.'
Miss Lawson said: 'I don't think it is the job of a woman to run a house.'
The barrister then said: 'This is no criticism of you as a domestic goddess.'
The celebrity cook took issue with the barrister referring to her as 'the lady of the house'.
Repeating the term back to her, Miss Lawson said: 'I don't think it is the job of a woman to run a house.'
The court was told that the former couple’s home had a 'silver room' - 12 feet by 12 feet - filled with tea services, candlesticks and trays.
The barrister said silver cleaners visited once or twice a month and charged £400 per visit.
When asked by Ms Arden about specialist cleaners who came to their homes, Miss Lawson said Mr Saatchi 'likes to have control over every element'.
She said: 'You make the wrong assumption if you think I was in control of the decisions, and I don't think for one minute your client would disagree with me.'
Speaking about weekends in which she would have been happy to spend time with the family and do her own washing up, Miss Lawson said she 'complied' with her ex-husband's decision to call in help.
The court also heard Charles only allowed his wife to have a dinner party at their Belgravia home once every two years.
Earlier in the trial, Nigella said that Charles was 'very much a cash man' and would have given Francesca money to take on trips for their children.