Police said Monday that "no further action" will be taken.
The 53-year-old Lawson told a court in December that she had used cocaine a handful of times but was not a regular user. She was testifying in the fraud case of two former aides.
A police statement says the decision was based on the need for police action to be "proportionate" and on whether further action would be in the public interest. The statement says further police action might deter victims from being candid with police and courts.
Police say they consulted prosecutors before deciding not to pursue charges.