Medication does have sulphur in it (5)
I believe the answer is:
doses
'medication does have sulphur in it' is the definition.
I can't tell whether this defines the answer.
'does have sulphur in it' is the wordplay.
I cannot really understand how this works, but
an anagram of 'does' is 'dose' which is within the answer.
'sulphur' could be 's' (synonyms) and 's' is found within the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for doses that I've seen before include "draughts" , "Prescribed quantities of medicine" , "Prescribed amounts of medicine" , "Administers medicine to (someone)" , "Gives medicine to" .)