Legal since 2018, medical cannabis requires a specialist prescription, usually...

https://iris-wiki.win/index.php/Will_the_List_of_Conditions_for_Medical_Cannabis_Expand_in_the_UK%3F_A_Reality_Check

Legal since 2018, medical cannabis requires a specialist prescription, usually after other standard treatments have failed. While NHS access is very limited, private clinics are currently the primary route