Norway sets statutory blood-concentration limits for 28 substances other than alcohol. This puts those numbers next to a decay curve, because the interesting part is not the limit itself. It is how long the limit outlasts the effects.
This cannot tell you whether it is safe or legal to drive, and it is not a defence. It does not know your blood concentration. Nobody does without a blood sample. Absorption, dose, purity, body composition, tolerance, liver function, urine pH and other drugs all move the numbers, and half-lives vary several-fold between people taking the same amount.
Being under a limit is also not the same as being unimpaired: the limits are legal thresholds, not a measure of how you are actually driving. Police measure blood, not arithmetic. If you have taken something and are wondering whether enough time has passed, the honest answer is that you cannot know, and the safe answer is not to drive.
Each tier is a different legal consequence, not a different degree of safety. Dropping under the 1.2 tier only means a lesser sentencing band; you are still over the limit until you are under the first one.
| Substance | Impairment (0.2‰) | 0.5‰ | 1.2‰ |
|---|
All values in µmol/L, exactly as the regulation states them. Where the two sentencing tiers are blank, the regulation deliberately sets none: the relationship between blood concentration and crash risk for that substance is too variable or too poorly documented to draw the line. Only the impairment limit applies.
Two numbers get confused constantly. The first is how long a drug is doing something. The second is how long it is detectable above a legal threshold. They are not the same number and the second is usually much larger, which is how people end up driving the morning after in the honest belief that they are fine.
An exponential decay makes that gap concrete. Every half-life halves what is left, so going from ten times the limit to under it takes a bit over three half-lives whatever the substance is. For something with a long half-life that is days, long after the last trace of an effect.
The other thing the table shows is that the limits are not set on one scale. They are calibrated per substance against what a given blood alcohol level does to driving, which is why they span five orders of magnitude, from 0.0006 µM for buprenorphine to 100 µM for GHB.
Limits from Forskrift om faste grenser for påvirkning av andre berusende eller bedøvende middel enn alkohol m.m. (FOR-2012-01-20-85), Vedlegg I, as amended. Half-life ranges are commonly cited textbook figures included as a starting point only; they vary widely between people and are not a property of you. This page runs entirely in your browser. Nothing is uploaded and nothing is stored.