Prescribed cannabis is legal, but the 2µg/L THC limit applies to all. A medical...

https://www.generate-bookmark.win/ev-driving-with-medical-cannabis-being-legal-doesn-t-excuse-impairment-you

Prescribed cannabis is legal, but the 2µg/L THC limit applies to all. A medical defence needs you to be unimpaired. You must tell the DVLA of your fitness. Legality isn't immunity; you remain responsible for safety