Tablets not really working, boy almost entirely covered in spots (8)
I believe the answer is:
placebos
'tablets not really working' is the definition.
I can't tell whether this defines the answer.
'boy almost entirely covered in spots' is the wordplay.
'almost entirely' means to remove the last letter (most but not all of the word).
'covered in' means one lot of letters goes inside another.
'spots' becomes 'places' ('place' can be a synonym of 'spot').
'boy' with its last letter taken away is 'bo'.
'bo' inserted inside 'places' is 'PLACEBOS'.
Can you help me to learn more?
(Other definitions for placebos that I've seen before include "Useless drugs" , "Inactive drugs" , "Medications with no medicinal content" , "Inert medications, given in drug trials" , "Physically inactive medicines" .)