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

https://atavi.com/share/xt53v2z1mxrjq

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.