Medical cannabis has been legal since 2018 but isn't a first-line option....

https://doctiplus.net/arthritis-and-medical-cannabis-can-uk-patients-get-a-prescription/

Medical cannabis has been legal since 2018 but isn't a first-line option. You’ll need a specialist assessment, usually via private clinics, once standard treatments have failed. Speak with a qualified professional to discuss your options.