Cannabis, driving and work
The two places where private use stops being private. What impairment actually does to driving, and why a test result is not the same as being high.
Almost everything about cannabis in South Africa is now a private matter between an adult and their own choices. There are two places where it stops being private, and both of them are worth being unambiguous about.
Driving
Do not drive after using cannabis. It is an offence, it always has been, and the Constitutional Court's protection of private use changed nothing about it.
Beyond the law, the reason is mechanical. Cannabis affects exactly the faculties driving runs on: reaction time, tracking — the small continuous corrections that keep a car in a lane — divided attention, and judgement of distance and speed. The effect is dose-related, and it is considerably worse in combination with alcohol than either is alone. Two things that each impair you a little do not add up; they multiply.
There is a particular trap with edibles, which come on slowly and last for hours. People who feel fine two hours after an edible are frequently not fine, because the peak had not arrived yet when they made the decision to drive.
How long should you wait?
Nobody can give you a number that is true for everyone, and anyone who does is guessing. What is honest:
- Inhaled cannabis peaks within about half an hour and its main effects fade over two to four hours — but measurable impairment can outlast the feeling of being high.
- Edibles can take two hours to arrive and run six to eight hours or more, sometimes with grogginess the next morning.
- Tolerance changes the felt experience, not necessarily the impairment. Feeling normal is not evidence of driving normally.
The workable rule is the one people use with alcohol and a big night: if you have used cannabis today, plan not to drive today. Arrange the lift before you use, not after.
A test is not a measure of being high
This confuses people, and it matters for both driving and work. THC is fat-soluble, and its metabolites linger long after any effect has gone — days for occasional users, potentially weeks for heavy daily ones.
So a urine test tells you somebody has used cannabis at some point recently. It does not tell you they are impaired now. Blood and saliva testing correlate better with recent use, but even there the relationship between a number and actual impairment is much weaker than it is for alcohol. Cannabis simply does not have a clean equivalent of a breathalyser reading.
The practical consequence: you can be entirely sober and still fail a test, and that is a real risk to plan around rather than argue with in the moment.
Work
Your employer's policy is a separate question from the law, and legalisation of private use did not rewrite it.
- Safety-sensitive work — driving, machinery, heights, electricity, healthcare — is where employers are strictest, usually with good reason.
- Many workplaces test, and a positive result can have consequences regardless of when you used or whether you were impaired.
- Know your policy before you need to. Reading it after an incident is the wrong order.
None of this is a moral position. It is that the private freedom South African law recognises is exactly that — private — and the moment you are on a public road or on somebody's payroll doing something dangerous, other people's safety is in the room with you.
