Prescribed cannabis is no immunity pass. While a medical defence exists, you...

https://evpowered.co.uk/feature/medical-cannabis-and-uk-driving-laws-what-ev-owners-must-know/

Prescribed cannabis is no immunity pass. While a medical defence exists, you must stay under the 2µg/L THC limit and meet DVLA standards. Legality never overrides responsibility; if impaired, you are liable, regardless of your prescription