Lawson was at the centre of lurid claims about drug-taking after an email from her estranged husband Charles Saatchi was used as evidence to defend Italian Elisabetta Grillo, 41, and her sister Francesca, 35. They were found not guilty yesterday.
The 53-year-old food writer was questioned at Isleworth Crown Court over the message, which referred to her being "off her head" on drugs. She later admitted to taking the Class A drug with her late husband, John Diamond, and during her marriage to Saatchi.
Lawson said she was "disappointed but unsurprised" by the jury's decision, adding that her experience as a witness had been "deeply disturbing".
In her statement, she added: "When false claims about habitual drug use were introduced, I did everything possible to ensure the CPS [Crown Prosecution Service] was aware of the sustained background campaign deliberately designed to destroy my reputation."
Scotland Yard said it would not be examining the allegations unless new evidence emerges.
A spokesman said: "Should any evidence - and that includes material from the trial - that could be investigated come to light, this decision will be reviewed."
Lawson had accused multi-millionaire art dealer Saatchi of threatening to "destroy" her. She said that, despite doing her civic duty by appearing in court, she was "maliciously vilified without the right to respond".
The sisters had been accused of spending more than £685,000 on themselves to live the "high life".
The court heard they used credit cards provided to them by the TV chef and her ex-husband to buy designer goods from Louis Vuitton, Christian Dior and Vivienne Westwood. Francesca was accused of spending the largest sum on herself - a total of £580,000.
However, the sisters insisted all of their purchases had been authorised. It was claimed by the defence there was a culture of secrecy within the high-profile couple's marriage and that the Grillo sisters were aware of Lawson's alleged drug use, while Saatchi was not.
The defence claimed that Elisabetta's knowledge of her employer's supposed drug use materially affected Lawson's attitude towards her spending.
After the three-week trial, the jury of seven men and five women rejected the prosecution's claims that the purchases on the cards had been unauthorised.
The jurors deliberated for nearly nine hours.
A delighted Francesca declared in Italian "There is a God!" after learning she had been found not guilty. Her barrister, Ms Arden, was seen in the court foyer, proclaiming to her client: "C'e un Dio!" Francesca replied with a smile: "C'e un Dio!" and the pair embraced.
Anthony Metzer, QC, representing Elisabetta, said his client was "relieved" and "crying her eyes out". Mr Metzer added he was "incredibly thrilled and delighted for both of them", and said he wanted to thank the jury for their attention during the trial. He added: "I'm a bit lost for words."
He said it had been a stressful case and that "medical issues" in relation to Elisabetta made it even harder.
Francesca Grillo's defence counsel, Karina Arden, said: "We're delighted with the result and the attention that the jury gave to the case over many hours and many days. We're reeling."
During the trial the jury heard details of Saatchi's email, in which Lawson was branded "Higella".
He said in that message: "Of course now the Grillos will get off on the basis that you ... were so off your heads on drugs that you allowed the sisters to spend whatever they liked and, yes, I believe every word the Grillos have said, who after all only stole money."
An original defence case statement for Elisabetta did not include allegations of Lawson's drug use because she did not want them raised in court as she felt sympathy for her, jurors heard. But an extra statement later did include the claims.
The additional statement, read to the court by Mr Metzer, said his client would assert that Ms Lawson "habitually indulged in the use of Class A and Class B drugs in addition to the abuse of prescription drugs" throughout the PA's employment.
Lawson admitted smoking cannabis, but said the suggestion she was a habitual user was "absolutely ridiculous". She described Saatchi as a "brilliant, but brutal man" who subjected her to "intimate terrorism".
l Prime Minister David Cameron said he had "probably said enough about his issue" after the verdict. He had been criticised by the judge for showing his support for Lawson during the trial.
He added: "I will plead the Fifth [amendment] about this one."