Laurence Gent, 19, appeared in Kaikohe District Court after THC was found in his blood in July and was ordered to pay $690 and disqualified for six months.
Patea Douglas Rakete, 30, appeared in Kaikohe District Court after THC was found in his blood in June and was sentenced to 40 hours' community work and disqualified for six months.
Zane Barrett Morgan Routledge, 18, was sentenced in Kaikohe District Court to a $500 fine and disqualified for six months after THC was found in his blood in August.
Peter John Reyland, 45, was ordered to pay $770 and disqualified for six months after he had THC in his blood in August.
Northland's top traffic cop, Inspector Murray Hodson, said earlier that police had been focusing on drug-impaired drivers, with more than 90 per cent of those tested found to have drugs in their system.
"That's a very high number and a real concern," he said.
While most of the busted Northland drivers were under the influence of cannabis, many had used methamphetamine.
Police can only drug-test drivers if they believe they are under the influence. The impairment test entails the driver having an eye assessment, followed by a walk and turn, and one-leg stand test.
Drivers who fail the test must undergo a blood test. At this stage there are no plans to introduce mouth swabs to detect drugs. Only officers trained to check for the signs of drug impairment were able to carry out tests.