For EV drivers using medical cannabis, a prescription offers a medical defence...

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

For EV drivers using medical cannabis, a prescription offers a medical defence but doesn't override the 2mcg/L THC limit. You must notify the DVLA of your fitness to drive. Remember: legality doesn’t replace responsibility—stay safe on the road.