Since 2018, medical cannabis has been legal in the UK for specific conditions....

https://post-wiki.win/index.php/Does_Marathon_Training_Count_as_a_Medical_Reason_for_a_Prescription%3F_A_Reality_Check_for_Runners

Since 2018, medical cannabis has been legal in the UK for specific conditions. Runners can access it via specialist private clinics if two previous treatments have failed