Jeffrey Chandler, spotted driving at 90mph near Penrith in June, tested positive for Class A and B drugs.
The 53-year-old, of Ventura Close, Manchester, admitted drug-impaired driving and possessing cannabis.
The judge at Carlisle Crown Court handed him a four-month prison sentence, suspended for 12 months.
Recorder Andrew Shaw said Chandler's drug readings indicated a "staggeringly high level of cocaine use".
He also ordered him to complete a rehabilitation requirement, a three-month night-time curfew and a 30-month driving ban.
A man was caught driving on the M6 under the influence of drugs when cannabis smoke from his car wafted into the vents of a following police car.