About Medicines, drugs and the yellow sticker: which statement is WRONG?
The standard is 'knows or ought to know that use can impair driving ability', not 'has a sticker'.
The law explicitly names any substance you know or ought to know can impair driving ability — that includes prescribed medicines just as much as illegal drugs, exactly why the yellow sticker appears on legal, pharmacy-obtained medication.
For combined use, each substance's limit becomes the lowest measurable amount: a zero-limit, lower than for single use.
A medicine you take only once is completely out of your system again after a few hours.
Explanation
trap: single-dose-is-short-lived. VekaBest p.16 — some medicines remain active in the body for up to 48 hours, even after a single use. 'Taken once' says nothing about how long driving ability stays affected