Prescribed cannabis users may have a medical defence against the 2µg/L THC...

https://www.mediafire.com/file/rkpx0pv3x6lgq5k/pdf-25878-69659.pdf/file

Prescribed cannabis users may have a medical defence against the 2µg/L THC limit, but it isn't a free pass. You must disclose your condition to the DVLA. Legal status never replaces the duty to drive safely. Impairment is impairment, prescription or not.