Medical cannabis users face a tricky road. A prescription offers a defence, but...

https://dlf-ne.org/can-i-drive-in-the-uk-if-i-have-a-medical-cannabis-prescription-the-reality-behind-the-wheel/

Medical cannabis users face a tricky road. A prescription offers a defence, but the 2mcg/L THC limit is absolute. Crucially, legal access doesn't bypass DVLA fitness to drive rules. Just because it’s prescribed doesn't remove your duty to drive unimpaired