The celebrity cook, who has admitted using cocaine and cannabis in the past, denied stashing the class A drug in a box containing her late husband's wedding rings as she gave evidence in the fraud trial of two of her former personal assistants.
"I promise you ... regular cocaine users do not look like this," she said. "They are scrawny and look unhealthy. If you think I'm going to sabotage my health and leave my children as orphans, you are very wrong."
Under cross-examination at Isleworth Crown Court in west London, Ms Lawson said she had "never knowingly" met a drug dealer and never exchanged money for cocaine.
"In my life, I'm reliable, professional and calm," she said. "I have no sense of being a drug taker of a habitual nature. I have owned up to drug use.
"If I was taking cocaine and cannabis to the extent you say, I wouldn't be standing here."
As questions of her drug use continued, Ms Lawson said: "I really feel if you want to put me on trial, put me on trial. I don't feel it is right to have me here as a witness for the Crown and treat me like this."
Karina Arden, representing defendant Francesca Grillo, accused Ms Lawson of "very regular use of cocaine" which "escalated in the last five years".
"That is categorically not the case," Ms Lawson replied. "My GP has seen me over a period of 10 to 12 years and he would know if these allegations held any truth."
Ms Lawson denied she kept cocaine in a hollow "fake book" alongside jewellery given to her by her mother and two grandmothers. The jewellery box also contained wedding rings she exchanged with her late husband John Diamond, including one he received after being diagnosed with terminal cancer, the court heard.
Ms Lawson's daughter and a friend discovered the box containing cocaine and called Francesca Grillo, who "tried to make up some sort of excuse to cover your back", Ms Arden put to Ms Lawson.
"No, I have never heard that," she replied.
The food writer was "in a high state of panic" after the book went missing when she moved house, Ms Arden added.
"I was in a high state of anxiety because I thought I had lost my late grandmothers' and late husband's jewellery and wedding rings," Ms Lawson replied. "It does not need embellishment."
Ms Lawson said it was "completely wrong" to suggest she frequently went downstairs at her home with white powder on her face or had a constant runny nose.
She admitted once joking about having a "cocaine habit" with a staff member as she applied make up.
Earlier Ms Lawson accused her multi-millionaire ex-husband of "peddling" stories about her alleged drug habit, including that he was checking her nose for cocaine when he was photographed gripping her throat outside Scott's restaurant in central London.
Ms Lawson said one of the reasons she did not start libel proceedings against Mr Saatchi was because she "can't afford it".
"I don't have a substantial fortune," she said. "I feel this is my last connection with him. I don't appreciate being bullied and I have been bullied."
Francesca Grillo, 35, and her sister Elisabetta, sometimes referred to as Lisa, 41, are accused of committing fraud by abusing their positions by using a company credit card for personal gain.
The pair are accused of using credit cards loaned to them by the TV cook and her former husband Mr Saatchi to spend more than £685,000 on themselves between 2008 and 2012, the jury has heard.
The Grillo sisters, of Bayswater, west London, deny the charge against them. The trial was adjourned until Tuesday.