Medical cannabis users have a defence against the 2mcg/L THC limit, but...

https://erickcmpc682.theglensecret.com/i-feel-fine-how-do-i-know-if-i-am-actually-safe-to-drive

Medical cannabis users have a defence against the 2mcg/L THC limit, but legality isn't immunity. You must stay fit to drive per DVLA rules. Being prescribed doesn't replace your duty to remain unimpaired. Responsibility remains yours, always.