Vital, but not to be had from chemist? (13)
I believe the answer is:
indispensable
'vital' is the definition.
(similar in meaning)
'not to be had from chemist?' is the wordplay.
I cannot quite understand how this works, but
'had' could be 'd' (in contractions e.g. 'I'd', 'you'd' etc) and 'd' is found within the answer.
'from' could be 'in' (I've seen this in other clues) and 'in' is found within the answer.
This explanation may well be incorrect...
'but' acts as a link.
Can you help me to learn more?
(Other definitions for indispensable that I've seen before include "Essential" , "Absolutely necessary" , "Vitally necessary" .)