Lawson told a London court on Thursday that "I would rather be honest and ashamed" than let false allegations stand."I wasn't going to be bullied with lies," she said. "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."
The celebrity chef was testifying for a second day at the fraud trial of two former assistants.
Elisabetta and Francesca Grillo, two sisters from Italy, are charged with using credit cards loaned to them by Lawson and her former husband Charles Saatchi to spend 685,000 pounds (more than $1 million) on luxury clothes, accessories and rooms at high-end hotels. They deny the fraud charges.
The case has been overshadowed by revelations about the troubled relationship between Lawson and Saatchi, a wealthy art collector. The couple divorced in July after Saatchi was photographed grabbing Lawson's throat outside a London restaurant.
Lawyers for the Grillos allege that Lawson sanctioned their high spending in exchange for their silence about her drug use. They have quoted an email in which Saatchi accused Lawson of being "so off her head" on drugs she allowed them to "spend whatever they liked."
On Wednesday, Lawson said she had taken cocaine a handful of times but denied being a regular drug user.
The trial has generated huge media interest. Lawson, 53, entered the court on Thursday walking past dozens of photographers and television cameras.
Cross-examined by Francesca Grillo's lawyer, Lawson denied using her court appearance to explain herself to the world's press or to hit back at her ex.
"I prefer to keep my private life private," she said. "I felt it was my duty to come."