People who have smoked marijuana days or weeks prior to having one of the new drug-driving tests that kick off in the Northern Territory today have no need to fear they will record a positive reading, police say.

The new drug tests will help police indentify people driving under the influence of cannabis or methamphetamine products such as speed, ice or ecstasy.

Cannabis can be detected in someone's system long after it is used, but Superintendent Bob Rennie from NT Police said the new tests only detected recent drug use.

"I have seen a lot in social media saying 'if I had a joint four days ago, [or] two weeks ago, it is still going to show up?' Well, no it won't because of the restrictions put on the testing regime," Superintendent Rennie said.

He said the tests only picked up the presence of cannabis that had been smoked in the five hours prior to the test being taken.

"If you have had a joint within five hours of being pulled up you may be at risk," he said.

Under the new testing, people who record a positive reading for driving under the influence of a drug on a first offence will receive a fine of about $400, which will escalate for subsequent offences and could include a $1,200 fine or six months imprisonment, Superintendent Rennie said.

Drug-driving tests have been underway in the NT for some time, but only for drivers of heavy vehicles.

National policy manager at the Australian Drug Foundation, Geoff Munro, backed the new tests.

Mr Munro said the tests were already being used in Victoria and NSW, and police commonly use them outside music festivals and when people are leaving entertainment precincts.

"One in 10 drivers tested in NSW are shown to have a drug in their system," Mr Munro said.

NT Transport Minister Peter Chandler said the laws aimed to reduce the number of people killed or seriously injured on the roads.

He said the move showed the Government had addressed concerns about drug use in the community and the need to implement tougher measures.