The celebrity chef, 53, said she had used cocaine a handful of times in her life, including when her late husband John Diamond was nearing the end of his life, as well in July 2010, when she said she was "subjected to intimate terrorism" by her now ex-husband Charles Saatchi.
She also admitted to smoking cannabis – at times, in front of her children – but denied being an addict.
"The idea that I'm a drug addict or a habitual user of cocaine is absolutely ridiculous," she said.
"I have to say, since freeing myself from a brilliant but brutal man, I'm now totally cannabis-, cocaine-, any drug-free," said added.
In addition, Lawson spoke about the incident over the summer in which Saatchi was photographed grabbing Lawson's throat.
She said that upon seeing a young child pass by she had commented on how much she looked forward to having grandchildren.
Lawson alleges that, in response, Saatchi grabbed her and said, "I am the only person you should be concerned with. I am the only person that should give you pleasure."
The celebrity chef's testimony wrapped for the day but she is expected back in court on Thursday.