'anti-medical' is formed from the prefix 'anti-' (from Greek 'anti' meaning 'against') combined with 'medical' (from Latin 'medicus' via Medieval Latin/Old French, relating to physicians or medicine).

'medical' derives from Latin 'medicus' ('physician') and Medieval Latin 'medicalis', passed into Old French as 'médical' and then into Middle/Modern English as 'medical'. The productive prefix 'anti-' comes from Greek 'anti-' in compounds and has been used in English since modern times to form oppositional adjectives; the compound 'anti-medical' is a modern formation applying 'anti-' to 'medical'.

Individually, 'medical' has long meant 'relating to physicians or medicine'; when combined with the prefix 'anti-' it gained the more specific modern sense 'opposed to medical treatment or the medical profession', used to describe attitudes, movements, or policies rejecting mainstream medical practice.