The simple answer is that a nanogram is equivalent to one billionth of a gram. A ng/mL stands for nanograms per milliliter. It is used by labs as a unit of measure of density for test results.
But what does it have to do with you using cannabis?
Since cannabis use is very likely to increase post-October 17, police could be using roadside tests to see if a driver is impaired. Based on Bill C-46, the update to Criminal Code regarding which included a section about driving under the influence of cannabis:
Less than 2 nanograms (ng) of THC per millilitre (mL) = no issue
2 nanograms (ng) but less than 5 ng of THC per millilitre (mL) of blood = max $1,000 fine
5 ng or more of THC per mL of blood =
First offence: mandatory minimum $1,000 fine
Second offence: mandatory minimum of 30 days imprisonment
Third and subsequent offences: mandatory minimum of 120 days imprisonment
The device acts as a breathalyzer, however, it tests the saliva and not the breath. The saliva test is for the presence of THC and the unit of measure is nanogram (ng). Drager 5000 is one such test devices and it has been selected by Department of Justice (DOJ) as a potential choice for police officers (it is important to note that currently there are many concerns about using this device for THC roadside tests).
When used, the officers will be taking a sample of the user’s saliva and testing for the presence of delta 9 THC. Delta 9 THC (Δ9-THC) is the molecule of cannabis that can be found specifically in the mouth after smoking.
Dräger DrugTest® 5000
Can you smoke "some" cannabis & be under 5 ng/mL? The answer is still very unclear.
"It would be great to be able to say, 'If you smoke one joint, you're okay, if you smoke two you're impaired,' but it's not that simple," says Dr. Robert Mann, a social and epidemiological research scientist at the Centre for Addiction and Mental Health (CAMH) interview with the Globe and Mail.
The big variable is the THC content – THC potency in dried cannabis has increased from an average of 3% in the 1980s to around 15% today. Some strains can have an average as high as 30% THC. The potency of THC in cannabis is often shown as a percentage of THC by weight (or by volume of an oil). Here are some examples:
Is this going to get less confusing at some point?
Health Canada is currently evaluating a number of approaches that could be used to effectively manage the concentration of THC in various cannabis products. It is the government's intention to set regulatory requirements that would standardize the amount of THC that could be in a single portion of certain cannabis products (for example, amount of THC per mL of cannabis oil) and that THC amounts be clearly stated on product labels. In this way, consumers will have clear information to make decisions about consumption and the risks they are taking.