Her claims came as the judge, Justice Robin Johnson, issued a rebuke to Prime Minister David Cameron over comments he made about the celebrity chef, urging the jury to reach its verdicts on the evidence alone.
Elisabetta Grillo, 41, one of the two PAs on trial, said she found various signs that Ms Lawson was using cocaine, including a packet of white powder found in a toilet in the home she shared with former husband, John Diamond, as well as rolled-up banknotes and credit cards with white powder on them.
Asked if she had ever seen the TV cook taking drugs, Ms Grillo - who is also known as Lisa - said "No".
But she told Isleworth Crown Court that she was aware that Ms Lawson had taken drugs and, when pressed by barrister Anthony Metzer QC about what type of substances, she said both cocaine and cannabis.She told the court she found similar evidence when Ms Lawson moved in with Mr Saatchi at his home in Eaton Square.
She said that in a drawer in Ms Lawson's office she found rolled-up banknotes.
Asked by Mr Metzer if there was anything on them, she said: " Yes, again, white stuff."
The defence barrister asked her how often over the years she had seen signs of drug use, to which she replied: "Regularly."
The Grillo sisters are accused of abusing their positions by spending £685,000 on credit cards belonging to the celebrity couple to buy designer goods and luxury holidays for themselves.
Elisabetta Grillo, 41, and sister Francesca, 35, of Kensington Gardens Square, Bayswater, west London, each deny a single count of committing fraud by using a company credit card for personal gain between January 1 2008 and December 31 last year.
The trial continues.